11. String expansions

Many strings in Exim's run time configuration are expanded before use. Some of them are expanded every time they are used; others are expanded only once.

When a string is being expanded it is copied verbatim from left to right except when a dollar or backslash character is encountered. A dollar specifies the start of a portion of the string which is interpreted and replaced as described below in section 11.4 onwards. Backslash is used as an escape character, as described in the following section.

11.1. Literal text in expanded strings

An uninterpreted dollar can be included in an expanded string by putting a backslash in front of it. A backslash can be used to prevent any special character being treated specially in an expansion, including itself. If the string appears in quotes in the configuration file, two backslashes are required because the quotes themselves cause interpretation of backslashes when the string is read in (see section 6.12).

A portion of the string can specified as non-expandable by placing it between two occurrences of \N. This is particularly useful for protecting regular expressions, which often contain backslashes and dollar signs. For example:

  deny senders = \N^\d{8}[a-z]@some\.site\.example$\N

On encountering the first \N, the expander copies subsequent characters without interpretation until it reaches the next \N or the end of the string.

11.2. Character escape sequences in expanded strings

A backslash followed by one of the letters ``n'', ``r'', or ``t'' in an expanded string is recognized as an escape sequence for the character newline, carriage return, or tab, respectively. A backslash followed by up to three octal digits is recognized as an octal encoding for a single character, and a backslash followed by ``x'' and up to two hexadecimal digits is a hexadecimal encoding.

These escape sequences are also recognized in quoted strings when they are read in. Their interpretation in expansions as well is useful for unquoted strings, and for other cases such as looked-up strings that are then expanded.

11.3. Testing string expansions

Many expansions can be tested by calling Exim with the -be option. This takes the command arguments, or lines from the standard input if there are no arguments, runs them through the string expansion code, and writes the results to the standard output. Variables based on configuration values are set up, but since no message is being processed, variables such as $local_part have no value. Nevertheless the -be option can be useful for checking out file and database lookups, and the use of expansion operators such as sg, substr and nhash.

Exim gives up its root privilege when it is called with the -be option, and instead runs under the uid and gid it was called with, to prevent users from using -be for reading files to which they do not have access.

11.4. Expansion items

The following items are recognized in expanded strings. White space may be used between sub-items that are keywords or substrings enclosed in braces inside an outer set of braces, to improve readability. Warning: Within braces, white space is significant.

$<variable name> or ${<variable name>}

Substitute the contents of the named variable, for example

  $local_part
  ${domain}

The second form can be used to separate the name from subsequent alphanumeric characters. This form (using curly brackets) is available only for variables; it does not apply to message headers. The names of the variables are given in section 11.8 below. If the name of a non-existent variable is given, the expansion fails.

${<op>:<string>}

The string is first itself expanded, and then the operation specified by <op> is applied to it. For example,

  ${lc:$local_part}

The string starts with the first character after the colon, which may be leading white space. A list of operators is given in section 11.5 below. The operator notation is used for simple expansion items that have just one argument, because it reduces the number of braces and therefore makes the string easier to understand.

${extract{<key>}{<string1>}{<string2>}{<string3>}}

The key and <string1> are first expanded separately. The key must not consist entirely of digits. The expanded <string1> must be of the form:

  <key1> = <value1> <key2> = <value2> ...

where the equals signs and spaces (but not both) are optional. If any of the values contain white space, they must be enclosed in double quotes, and any values that are enclosed in double quotes are subject to escape processing as described in section 6.12. The expanded <string1> is searched for the value that corresponds to the key. The search is case-insensitive. If the key is found, <string2> is expanded, and replaces the whole item; otherwise <string3> is used. During the expansion of <string2> the variable $value contains the value that has been extracted. Afterwards, it is restored to any previous value it might have had.

If {<string3>} is omitted, the item is replaced by an empty string if the key is not found. If {<string2>} is also omitted, the value that was extracted is used. Thus, for example, these two expansions are identical, and yield ``2001'':

  ${extract{gid}{uid=1984 gid=2001}}
  ${extract{gid}{uid=1984 gid=2001}{$value}}

Instead of {<string3>} the word ``fail'' (not in curly brackets) can appear, for example:

  ${extract{Z}{A=... B=...}{$value} fail }

{<string2>} must be present for ``fail'' to be recognized. When this syntax is used, if the extraction fails, the entire string expansion fails in a way that can be detected by the code in Exim which requested the expansion. This is called ``forced expansion failure'', and its consequences depend on the circumstances. In some cases it is no different from any other expansion failure, but in others a different action may be taken. Such variations are mentioned in the documentation of the option which is expanded.

${extract{<number>}{<separators>}{<string1>}{<string2>}{<string3>}}

The <number> argument must consist entirely of decimal digits. This is what distinguishes this form of extract from the previous kind. It behaves in the same way, except that, instead of extracting a named field, it extracts from <string1> the field whose number is given as the first argument. You can use $value in <string2> or fail instead of <string3> as before.

The first field is numbered one. If the number is negative, the fields are counted from the end of the string, with the rightmost one numbered -1. If the number given is zero, the entire string is returned. If the modulus of the number is greater than the number of fields in the string, the result is the expansion of <string3>, or the empty string if <string3> is not provided. The fields in the string are separated by any one of the characters in the separator string. For example:

  ${extract{2}{:}{x:42:99:& Mailer::/bin/bash}}

yields ``42'', and

  ${extract{-4}{:}{x:42:99:& Mailer::/bin/bash}}

yields ``99''. Two successive separators mean that the field between them is empty (for example, the fifth field above).

  abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQWRSTUVWXYZ0123456789

$header_<header name>: or $h_<header name>:
$rheader_<header name>: or $rh_<header name>:

  $header_reply-to:

The newline that terminates a header line is not included in the expansion, but internal newlines (caused by splitting the header line over several physical lines) may be present. The difference between header and rheader is that the latter inserts the ``raw'' contents of header lines without the removal of leading and trailing whitespace.

Header names follow the syntax of RFC 2822, which states that they may contain any printing characters except space and colon. Consequently, curly brackets do not terminate header names, and should not be used to enclose them as if they were variables. Attempting to do so causes a syntax error.

Only header lines that are common to all copies of a message are visible to this mechanism. These are the original header lines that are received with the message, and any that are added by an ACL warn statement or by a system filter. Header lines that are added to a particular copy of a message by a router or transport are not accessible.

For incoming SMTP messages, no header lines are visible in ACLs that are obeyed before the DATA ACL, because the header structure is not set up until the message is received. Header lines that are added by warn statements in a RCPT ACL (for example) are saved until the message's incoming header lines are available, at which point they are added. When a DATA ACL is running, however, header lines added by earlier ACLs are visible.

Upper case and lower case letters are synonymous in header names. If the following character is white space, the terminating colon may be omitted, but this is not recommended, because you may then forget it when it is needed. When white space terminates the header name, it is included in the expanded string. If the message does not contain the given header, the expansion item is replaced by an empty string. (See the def condition in section 11.6 for a means of testing for the existence of a header.)

If there is more than one header with the same name, they are all concatenated to form the substitution string, up to a maximum length of 64K. A newline character is inserted between each line. For the header expansion, for those headers that contain lists of addresses, a comma is also inserted at the junctions between lines. This does not happen for the rheader expansion.

  ${hmac{md5}{somesecret}{$primary_hostname $tod_log}}

  dd97e3ba5d1a61b5006108f8c8252953

  SPAMSCAN_SECRET=cohgheeLei2thahw

  headers_add = \
    X-Spam-Scanned: ${primary_hostname} ${message_id} \
    ${hmac{md5}{SPAMSCAN_SECRET}\
    {${primary_hostname},${message_id},$h_message-id:}}

Then given a message, you can check where it was scanned by looking at the X-Spam-Scanned: header line. If you know the secret, you can check that this header line is authentic by recomputing the authentication code from the host name, message ID and the Message-id: header line. This can be done using Exim's -be option, or by other means, for example by using the hmac_md5_hex() function in Perl.

${if <condition> {<string1>}{<string2>}}

If <condition> is true, <string1> is expanded and replaces the whole item; otherwise <string2> is used. For example,

  ${if eq {$local_part}{postmaster} {yes}{no} }

The second string need not be present; if it is not and the condition is not true, the item is replaced with nothing. Alternatively, the word ``fail'' may be present instead of the second string (without any curly brackets). In this case, the expansion is forced to fail if the condition is not true. The available conditions are described in section 11.6 below.

The result of this item is either the first <n> characters or the whole of <string2>, whichever is the shorter. Do not confuse length with strlen, which gives the length of a string.

${lookup{<key>} <search type> {<file>} {<string1>} {<string2>}}
${lookup <search type> {<query>} {<string1>} {<string2>}}

These items specify data lookups in files and databases, as discussed in chapter 9. The first form is used for single-key lookups, and the second is used for query-style lookups. The <key>, <file>, and <query> strings are expanded before use.

If there is any white space in a lookup item which is part of a filter command, a retry or rewrite rule, a routing rule for the manualroute router, or any other place where white space is significant, the lookup item must be enclosed in double quotes. The use of data lookups in users' filter files may be locked out by the system administrator.

If the lookup succeeds, <string1> is expanded and replaces the entire item. During its expansion, the variable $value contains the data returned by the lookup. Afterwards it reverts to the value it had previously (at the outer level it is empty). If the lookup fails, <string2> is expanded and replaces the entire item. If {<string2>} is omitted, the replacement is null on failure. Alternatively, <string2> can itself be a nested lookup, thus providing a mechanism for looking up a default value when the original lookup fails.

If a nested lookup is used as part of <string1>, $value contains the data for the outer lookup while the parameters of the second lookup are expanded, and also while <string2> of the second lookup is expanded, should the second lookup fail.

Instead of {<string2>} the word ``fail'' can appear, and in this case, if the lookup fails, the entire expansion is forced to fail. If both {<string1>} and {<string2>} are omitted, the result is the looked up value in the case of a successful lookup, and nothing in the case of failure.

For single-key lookups, the string ``partial'' is permitted to precede the search type in order to do partial matching, and * or *@ may follow a search type to request default lookups if the key does not match (see sections 9.5 and 9.6 for details).

If a partial search is used, the variables $1 and $2 contain the wild and non-wild parts of the key during the expansion of the replacement text. They return to their previous values at the end of the lookup item.

This example looks up the postmaster alias in the conventional alias file:

  ${lookup {postmaster} lsearch {/etc/aliases} {$value}}

This example uses NIS+ to look up the full name of the user corresponding to the local part of an address, forcing the expansion to fail if it is not found:

  ${lookup nisplus {[name=$local_part],passwd.org_dir:gcos} \
    {$value}fail}

  ${nhash{8}{64}{supercalifragilisticexpialidocious}}

returns the string ``6/33''.

${perl{<subroutine>}{<arg>}{<arg>}...}

This item is available only if Exim has been built to include an embedded Perl interpreter. The subroutine name and the arguments are first separately expanded, and then the Perl subroutine is called with those arguments. No additional arguments need be given; the maximum number permitted, including the name of the subroutine, is nine.

The return value of the subroutine is inserted into the expanded string, unless the return value is undef. In that case, the expansion fails in the same way as an explicit ``fail'' on a lookup item. The return value is a scalar. Whatever you return is evaluated in a scalar context. For example, if you return the name of a Perl vector, the return value is the size of the vector, not its contents.

If the subroutine exits by calling Perl's die function, the expansion fails with the error message that was passed to die. More details of the embedded Perl facility are given in chapter 12.

The redirect router has an option called forbid_filter_perl which locks out the use of this expansion item in filter files.

${readfile{<file name>}{<eol string>}}

The file name and end-of-line string are first expanded separately. The file is then read, and its contents replace the entire item. All newline characters in the file are replaced by the end-of-line string if it is present. Otherwise, newlines are left in the string. String expansion is not applied to the contents of the file. If you want this, you must wrap the item in an expand operator. If the file cannot be read, the string expansion fails.

The redirect router has an option called forbid_filter_readfile which locks out the use of this expansion item in filter files.

  ${readsocket{/socket/name}{request string}}

  ${readsocket{/socket/name}{request-string}{3s}}

  ${readsocket{/socket/name}{request-string}{3s}{ }}

  ${readsocket{/socket/name}{request-string}{3s}{\n}\
    {socket failure}}

The redirect router has an option called forbid_filter_readsocket which locks out the use of this expansion item in filter files.

This item inserts ``raw'' header lines. It is described with the header expansion item above.

${run{<command> <args>}{<string1>}{<string2>}}

The command and its arguments are first expanded separately, and then the command is run in a separate process, but under the same uid and gid. As in other command executions from Exim, a shell is not used by default. If you want a shell, you must explicitly code it. If the command succeeds (gives a zero return code) <string1> is expanded and replaces the entire item; during this expansion, the standard output from the command is in the variable $value. If the command fails, <string2>, if present, is expanded. If it is absent, the result is empty. Alternatively, <string2> can be the word ``fail'' (not in braces) to force expansion failure if the command does not succeed. If both strings are omitted, the result is the standard output on success, and nothing on failure.

The return code from the command is put in the variable $runrc, and this remains set afterwards, so in a filter file you can do things like this:

  if "${run{x y z}{}}$runrc" is 1 then ...
    elif $runrc is 2 then ...
    ...
  endif

Warning: In a router or transport, you cannot assume the order in which option values are expanded, except for those pre-conditions whose order of testing is documented. Therefore, you cannot reliably expect to set $runrc by the expansion of one option, and use it in another.

The redirect router has an option called forbid_filter_run which locks out the use of this expansion item in filter files.

${sg{<subject>}{<regex>}{<replacement>}}

This item works like Perl's substitution operator (s) with the global (/g) option; hence its name. However, unlike the Perl equivalent, Exim does not modify the subject string; instead it returns the modified string for insertion into the overall expansion. The item takes three arguments: the subject string, a regular expression, and a substitution string. For example

  ${sg{abcdefabcdef}{abc}{xyz}}

yields ``xyzdefxyzdef''. Because all three arguments are expanded before use, if any $ or \ characters are required in the regular expression or in the substitution string, they have to be escaped. For example

  ${sg{abcdef}{^(...)(...)\$}{\$2\$1}}

yields ``defabc'', and

  ${sg{1=A 4=D 3=C}{\N(\d+)=\N}{K\$1=}}

yields ``K1=A K4=D K3=C''. Note the use of \N to protect the contents of the regular expression from string expansion.

  ${substr{3}{2}{$local_part}}

  ${substr{-5}{2}{1234567}}

  ${substr{-5}{2}{12}}

  ${substr{-3}{2}{12}}

If the second number is omitted from substr, the remainder of the string is taken if the offset was positive. If it was negative, all characters in the string preceding the offset point are taken. For example, an offset of -1 and no length yields all but the last character of the string.

${tr{<subject>}{<characters>}{<replacements>}}

This item does single-character translation on its subject string. The second argument is a list of characters to be translated in the subject string. Each matching character is replaced by the corresponding character from the replacement list. For example

  ${tr{abcdea}{ac}{13}}

yields ``1b3de1''. If there are duplicates in the second character string, the last occurrence is used. If the third string is shorter than the second, its last character is replicated. However, if it is empty, no translation takes place.

11.5. Expansion operators

For expansion items that perform transformations on a single argument string, the ``operator'' notation is used because it is simpler and uses fewer braces. The substring is first expanded before the operation is applied to it. The following operations can be performed:

${address:<string>}

The string is interpreted as an RFC 2822 address, as it might appear in a header line, and the effective address is extracted from it. If the string does not parse successfully, the result is empty.

${base62:<digits>}

The string must consist entirely of decimal digits. The number is converted to base 62 (sic) and output as a string of six characters, including leading zeros. Note: Just to be absolutely clear: this is not base64 encoding.

${domain:<string>}

The string is interpreted as an RFC 2822 address and the domain is extracted from it. If the string does not parse successfully, the result is empty.

${escape:<string>}

If the string contains any non-printing characters, they are converted to escape sequences starting with a backslash. Whether characters with the most significant bit set (so-called ``8-bit characters'') count as printing or not is controlled by the print_topbitchars option.

  deny   message = Too many bad recipients
         condition =                    \
           ${if and {                   \
             {>{$rcpt_count}{10}}       \
             {                          \
             <                          \
               {$recipients_count}      \
               {${eval:$rcpt_count/2}}  \
             }                          \
           }{yes}{no}}

The condition is true if there have been more than 10 RCPT commands and fewer than half of them have resulted in a valid recipient.

${expand:<string>}

The expand operator causes a string to be expanded for a second time. For example,

  ${expand:${lookup{$domain}dbm{/some/file}{$value}}}

first looks up a string in a file while expanding the operand for expand, and then re-expands what it has found.

The world is slowly moving towards Unicode, although there are no standards for email yet. However, other applications (including some databases) are starting to store data in Unicode, using UTF-8 encoding. The Unicode code points with values less than 256 are compatible with ASCII and ISO-8859-1 (also known as Latin-1), which of course are single-byte encodings. This operator converts from a UTF-8 string to an ISO-8859-1 string. UTF-8 code values greater than 255 are converted to underscores. The input must be a valid UTF-8 string. If it is not, the result is an undefined sequence of bytes.

${hash_<n>_<m>:<string>}

The hash operator is a simpler interface to the hashing function that can be used when the two parameters are fixed numbers (as opposed to strings that change when expanded). The effect is the same as

See the description of the general hash item above for details. The abbreviation h can be used when hash is used as an operator.

This operator converts a hex string into one that is base64 encoded. This can be useful for processing the output of the MD5 and SHA-1 hashing functions.

${lc:<string>}

This forces the letters in the string into lower-case, for example:

  ${lc:$local_part}

${length_<number>:<string>}

The length operator is a simpler interface to the length function that can be used when the parameter is a fixed number (as opposed to a string that changes when expanded). The effect is the same as

See the description of the general length item above for details. Note that length is not the same as strlen. The abbreviation l can be used when length is used as an operator.

${local_part:<string>}

The string is interpreted as an RFC 2822 address and the local part is extracted from it. If the string does not parse successfully, the result is empty.

${mask:<IP address>/<bit count>}

If the form of the string to be operated on is not an IP address followed by a slash and an integer (that is, a network address in CIDR notation), the expansion fails. Otherwise, this operator converts the IP address to binary, masks off the least significant bits according to the bit count, and converts the result back to text, with mask appended. For example,

  ${mask:10.111.131.206/28}

returns the string ``10.111.131.192/28''. Since this operation is expected to be mostly used for looking up masked addresses in files, the result for an IPv6 address uses dots to separate components instead of colons, because colon terminates a key string in lsearch files. So, for example,

  ${mask:3ffe:ffff:836f:0a00:000a:0800:200a:c031/99}

returns the string

  3ffe.ffff.836f.0a00.000a.0800.2000.0000/99

Letters in IPv6 addresses are always output in lower case.

${md5:<string>}

The md5 operator computes the MD5 hash value of the string, and returns it as a 32-digit hexadecimal number, in which any letters are in lower case.

${nhash_<n>_<m>:<string>}

The nhash operator is a simpler interface to the numeric hashing function that can be used when the two parameters are fixed numbers (as opposed to strings that change when expanded). The effect is the same as

See the description of the general nhash item above for details.

${quote:<string>}

The quote operator puts its argument into double quotes if it contains anything other than letters, digits, underscores, full stops (periods), and hyphens. Any occurrences of double quotes and backslashes are escaped with a backslash. Newlines and carriage returns are converted to \n and \r, respectively For example,

  ${quote:ab"*"cd}

becomes

  "ab\"*\"cd"

The place where this is useful is when the argument is a substitution from a variable or a message header. In particular, if you are creating a new email address from the contents of $local_part (or any other unknown data), you should always use this operator.

${quote_<lookup-type>:<string>}

This operator applies lookup-specific quoting rules to the string. Each query-style lookup type has its own quoting rules which are described with the lookups in chapter 9. For example,

  ${quote_ldap:two + two}

returns ``two%20%5C+%20two''. For single-key lookup types, no quoting is necessary and this operator yields an unchanged string.

${rxquote:<string>}

The rxquote operator inserts a backslash before any non-alphanumeric characters in its argument. This is useful when substituting the values of variables or headers inside regular expressions.

  ? = ( ) < > @ , ; : \ " . [ ] _ 

The item is replace by the length of the expanded string, expressed as a decimal number. Note: Do not confuse strlen with length.

${substr_<start>_<length>:<string>}

The substr operator is a simpler interface to the substr function that can be used when the two parameters are fixed numbers (as opposed to strings that change when expanded). The effect is the same as

See the description of the general substr item above for details. The abbreviation s can be used when substr is used as an operator.

${uc:<string>}

This forces the letters in the string into upper-case.

11.6. Expansion conditions

The following conditions are available for testing by the ${if construct while expanding strings:

!<condition>

Preceding any condition with an exclamation mark negates the result of the condition.

<symbolic operator> {<string1>}{<string2>}

There are a number of symbolic operators for doing numeric comparisons. They are:

=	equal
==	equal
>	greater
>=	greater or equal
<	less
<=	less or equal

For example,

  ${if >{$message_size}{10M} ...

Note that the general negation operator provides for inequality testing. The two strings must take the form of optionally signed decimal integers, optionally followed by one of the letters ``K'' or ``M'' (in either upper or lower case), signifying multiplication by 1024 or 1024*1024, respectively.

crypteq {<string1>}{<string2>}

This condition is included in the Exim binary if it is built to support any authentication mechanisms (see chapter 32). Otherwise, it is necessary to define SUPPORT_CRYPTEQ in Local/Makefile to get crypteq included in the binary.

The crypteq condition has two arguments. The first is encrypted and compared against the second, which is already encrypted. The second string may be in the LDAP form for storing encrypted strings, which starts with the encryption type in curly brackets, followed by the data. If the second string does not begin with ``{'' it is assumed to be encrypted with crypt() or crypt16() (see below), since such strings cannot begin with ``{''. Typically this will be a field from a password file.

An example of an encrypted string in LDAP form is:

  {md5}CY9rzUYh03PK3k6DJie09g==

If such a string appears directly in an expansion, the curly brackets have to be quoted, because they are part of the expansion syntax. For example:

  ${if crypteq {test}{\{md5\}CY9rzUYh03PK3k6DJie09g==}{yes}{no}}

The following encryption types are supported:

• {md5} computes the MD5 digest of the first string, and expresses this as printable characters to compare with the remainder of the second string. If the length of the comparison string is 24, Exim assumes that it is base64 encoded (as in the above example). If the length is 32, Exim assumes that it is a hexadecimal encoding of the MD5 digest. If the length not 24 or 32, the comparison fails.

• {sha1} computes the SHA-1 digest of the first string, and expresses this as printable characters to compare with the remainder of the second string. If the length of the comparison string is 28, Exim assumes that it is base64 encoded. If the length is 40, Exim assumes that it is a hexadecimal encoding of the SHA-1 digest. If the length is not 28 or 40, the comparison fails.

• {crypt} calls the crypt() function, which uses only the first eight characters of the password.

• {crypt16} calls the crypt16() function (also known as bigcrypt()), which uses up to 16 characters of the password.

Exim has its own version of crypt16() (which is just a double call to crypt()). For operating systems that have their own version, setting HAVE_CRYPT16 in Local/Makefile when building Exim causes it to use the operating system version instead of its own. This option is set by default in the OS-dependent Makefile for those operating systems that are known to support crypt16().

Note that if a password is no longer than 8 characters, the results of encrypting it with crypt() and crypt16() are identical. That means that crypt16() is backwards compatible, as long as nobody feeds it a password longer than 8 characters.

def:<variable name>

The def condition must be followed by the name of one of the expansion variables defined in section 11.8. The condition is true if the named expansion variable does not contain the empty string, for example

  ${if def:sender_ident {from $sender_ident}}

Note that the variable name is given without a leading $ character. If the variable does not exist, the expansion fails.

def:header_<header name>:  or  def:h_<header name>:

This condition is true if a message is being processed and the named header exists in the message. For example,

  ${if def:header_reply-to:{$h_reply-to:}{$h_from:}}

Note that no $ appears before header_ or h_ in the condition, and that header names must be terminated by colons if white space does not follow.

eq {<string1>}{<string2>}

The two substrings are first expanded. The condition is true if the two resulting strings are identical, including the case of letters. Use the lc or uc expansion operators to force both strings to the same case if you want to do a caseless comparison.

exists {<file name>}

The substring is first expanded and then interpreted as an absolute path. The condition is true if the named file (or directory) exists. The existence test is done by calling the stat() function. The use of the exists test in users' filter files may be locked out by the system administrator.

first_delivery

This condition, which has no data, is true during a message's first delivery attempt. It is false during any subsequent delivery attempts.

ldapauth {<ldap query>}

This condition supports user authentication using LDAP. See section 9.10 for details of how to use LDAP in lookups and the syntax of queries. For this use, the query must contain a user name and password. The query itself is not used, and can be empty. The condition is true if the password is not empty, and the user name and password are accepted by the LDAP server. An empty password is rejected without calling LDAP because LDAP binds with an empty password are considered anonymous regardless of the username, and will succeed in most configurations. See chapter 32 for details of SMTP authentication, and chapter 33 for an example of how this can be used.

match {<string1>}{<string2>}

The two substrings are first expanded. The second is then treated as a regular expression and applied to the first. Because of the pre-expansion, if the regular expression contains dollar, or backslash characters, they must be escaped. Care must also be taken if the regular expression contains braces (curly brackets). A closing brace must be escaped so that it is not taken as a premature termination of <string2>. The easiest approach is to use the \N feature to disable expansion of the regular expression. For example,

  ${if match {$local_part}{\N^\d{3}\N} ...

If the whole expansion string is in double quotes, further escaping of backslashes is also required.

The condition is true if the regular expression match succeeds. At the start of an if expansion the values of the numeric variable substitutions $1 etc. are remembered. Obeying a match condition that succeeds causes them to be reset to the substrings of that condition and they will have these values during the expansion of the success string. At the end of the if expansion, the previous values are restored. After testing a combination of conditions using or, the subsequent values of the numeric variables are those of the condition that succeeded.

pam {<string1>:<string2>:...}

Pluggable Authentication Modules (http://www.kernel.org/pub/linux/libs/pam/) are a facility which is available in the latest releases of Solaris and in some GNU/Linux distributions. The Exim support, which is intended for use in conjunction with the SMTP AUTH command, is available only if Exim is compiled with

  SUPPORT_PAM=yes

in Local/Makefile. You probably need to add -lpam to EXTRALIBS, and in some releases of GNU/Linux -ldl is also needed.

The argument string is first expanded, and the result must be a colon-separated list of strings. The PAM module is initialized with the service name ``exim'' and the user name taken from the first item in the colon-separated data string (<string1>). The remaining items in the data string are passed over in response to requests from the authentication function. In the simple case there will only be one request, for a password, so the data consists of just two strings.

There can be problems if any of the strings are permitted to contain colon characters. In the usual way, these have to be doubled to avoid being taken as separators. If the data is being inserted from a variable, the sg expansion item can be used to double any existing colons. For example, the configuration of a LOGIN authenticator might contain this setting:

  server_condition = ${if pam{$1:${sg{$2}{:}{::}}}{yes}{no}}

For a PLAIN authenticator you could use:

  server_condition = ${if pam{$2:${sg{$3}{:}{::}}}{yes}{no}}

In some operating systems, PAM authentication can be done only from a process running as root. Since Exim is running as the Exim user when receiving messages, this means that PAM cannot be used directly in those systems. A patched version of the pam_unix module that comes with the Linux PAM package is available from http://www.e-admin.de/pam_exim/. The patched module allows one special uid/gid combination, in addition to root, to authenticate. If you build the patched module to allow the Exim user and group, PAM can then be used from an Exim authenticator.

pwcheck {<string1>:<string2>}

This condition supports user authentication using the Cyrus pwcheck daemon. This is one way of making it possible for passwords to be checked by a process that is not running as root.

The pwcheck support is not included in Exim by default. You need to specify the location of the pwcheck daemon's socket in Local/Makefile before building Exim. For example:

  CYRUS_PWCHECK_SOCKET=/var/pwcheck/pwcheck

You do not need to install the full Cyrus software suite in order to use the pwcheck daemon. You can compile and install just the daemon alone from the Cyrus SASL library. Ensure that exim is the only user that has access to the /var/pwcheck directory.

The pwcheck condition takes one argument, which must be the user name and password, separated by a colon. For example, in a LOGIN authenticator configuration, you might have this:

  server_condition = ${if pwcheck{$1:$2}{1}{0}}

queue_running

This condition, which has no data, is true during delivery attempts that are initiated by queue runner processes, and false otherwise.

radius {<authentication string>}

Radius authentication (RFC 2865) is supported in a similar way to PAM. You must set RADIUS_CONFIG_FILE in Local/Makefile to specify the location of the Radius client configuration file in order to build Exim with Radius support. You may also have to supply a suitable setting in EXTRALIBS so that the Radius library can be found when Exim is linked. The string specified by RADIUS_CONFIG_FILE is expanded and passed to the Radius client library, which calls the Radius server. The condition is true if the authentication is successful. For example

  server_condition = ${if radius{<arguments>}{yes}{no}}

11.7. Combining expansion conditions

Several conditions can be tested at once by combining them using the and and or combination conditions. Note that and and or are complete conditions on their own, and precede their lists of sub-conditions. Each sub-condition must be enclosed in braces within the overall braces that contain the list. No repetition of if is used.

or {{<cond1>}{<cond2>}...}

The sub-conditions are evaluated from left to right. The condition is true if any one of the sub-conditions is true. For example,

  ${if or {{eq{$local_part}{spqr}}{eq{$domain}{testing.com}}}...

When a true sub-condition is found, the following ones are parsed but not evaluated. If there are several ``match'' sub-conditions the values of the numeric variables afterwards are taken from the first one that succeeds.

and {{<cond1>}{<cond2>}...}

The sub-conditions are evaluated from left to right. The condition is true if all of the sub-conditions are true. If there are several ``match'' sub-conditions, the values of the numeric variables afterwards are taken from the last one. When a false sub-condition is found, the following ones are parsed but not evaluated.

11.8. Expansion variables

The variables that are available for use in expansion strings are:

$0, $1, etc: When a match expansion condition succeeds, these variables contain the captured substrings identified by the regular expression during subsequent processing of the success string of the containing if expansion item. They may also be set externally by some other matching process which precedes the expansion of the string. For example, the commands available in Exim filter files include an if command with its own regular expression matching condition.

$acl_m0 - $acl_m9: Values can be placed in these variables by the set modifier in an ACL. They retain their values while a message is being received, including during the running of a local_scan() function, but are reset afterwards. They are also reset by MAIL, RSET, EHLO, HELO, and after starting a TLS session.

$acl_verify_message: During the expansion of the message modifier in an ACL statement after an address verification has failed, this variable contains the original failure message that will be overridden by the expanded string.

$address_data: This variable is set by means of the address_data option in routers. The value then remains with the address while it is processed by subsequent routers and eventually a transport. If the transport is handling multiple addresses, the value from the first address is used. See chapter 14 for more details. Note: the contents of $address_data are visible in user filter files.

If $address_data is set when the routers are called to verify an address from an ACL, the final value remains available in subsequent conditions in the ACL statement. If routing the address caused it to be redirected to a single address, the child address is also routed as part of the verification, and in this case the final value of $address_data is from the child's routing.

$address_file: When, as a result of aliasing or forwarding, a message is directed to a specific file, this variable holds the name of the file when the transport is running. For example, using the default configuration, if user r2d2 has a .forward file containing

  /home/r2d2/savemail

then when the address_file transport is running, $address_file contains ``/home/r2d2/savemail''. At other times, the variable is empty.

$address_pipe: When, as a result of aliasing or forwarding, a message is directed to a pipe, this variable holds the pipe command when the transport is running.

$authenticated_id: When a server successfully authenticates a client it may be configured to preserve some of the authentication information in the variable $authenticated_id (see chapter 32). For example, a user/password authenticator configuration might preserve the user name for use in the routers. When a message is submitted locally (that is, not over a TCP connection), the value of $authenticated_id is the login name of the calling process.

$authenticated_sender: When a client host has authenticated itself, Exim pays attention to the AUTH= parameter on the SMTP MAIL command, provided the setting of server_mail_auth_condition (see chapter 32) permits it. Otherwise, it accepts the syntax, but ignores the data. Unless the data is the string ``<>'', it is set as the authenticated sender of the message, and the value is available during delivery in the $authenticated_sender variable. When a message is submitted locally (that is, not over a TCP connection), the value of $authenticated_sender is an address constructed from the login name of the calling process and $qualify_domain.

$authentication_failed: This variable is set to ``1'' in an Exim server if a client issues an AUTH command that does not succeed. Otherwise it is set to ``0''. This makes it possible to distinguish between ``did not try to authenticate'' ($sender_host_authenticated is empty and $authentication_failed is set to ``0'') and ``tried to authenticate but failed'' ($sender_host_authenticated is empty and $authentication_failed is set to ``1''). Failure includes any negative response to an AUTH command, including (for example) an attempt to use an undefined mechanism.

$body_linecount: When a message is being received or delivered, this variable contains the number of lines in the message's body.

$bounce_recipient: This is set to the recipient address of a bounce message while Exim is creating it. It is useful if a customized bounce message text file is in use (see chapter 40).

$caller_gid: The group id under which the process that called Exim was running. This is not the same as the group id of the originator of a message (see $originator_gid). If Exim re-execs itself, this variable in the new incarnation normally contains the Exim gid.

$caller_uid: The user id under which the process that called Exim was running. This is not the same as the user id of the originator of a message (see $originator_uid). If Exim re-execs itself, this variable in the new incarnation normally contains the Exim uid.

$compile_date: The date on which the Exim binary was compiled.

$compile_number: The building process for Exim keeps a count of the number of times it has been compiled. This serves to distinguish different compilations of the same version of the program.

$dnslist_domain: When a client host is found to be on a DNS (black) list, the list's domain name is put into this variable so that it can be included in the rejection message.

$dnslist_text: When a client host is found to be on a DNS (black) list, the contents of any associated TXT record are placed in this variable.

$dnslist_value: When a client host is found to be on a DNS (black) list, the IP address from the resource record is placed in this variable.

$domain: When an address is being routed, or delivered on its own, this variable contains the domain. Global address rewriting happens when a message is received, so the value of $domain during routing and delivery is the value after rewriting. $domain is set during user filtering, but not during system filtering, because a message may have many recipients and the system filter is called just once.

When more than one address is being delivered at once (for example, several RCPT commands in one SMTP delivery), $domain is set only if they all have the same domain. Transports can be restricted to handling only one domain at a time if the value of $domain is required at transport time - this is the default for local transports. For further details of the environment in which local transports are run, see chapter 22.

At the end of a delivery, if all deferred addresses have the same domain, it is set in $domain during the expansion of delay_warning_condition.

The $domain variable is also used in some other circumstances:

• When an ACL is running for a RCPT command, $domain contains the domain of the recipient address.

• When a rewrite item is being processed (see chapter 30), $domain contains the domain portion of the address that is being rewritten; it can be used in the expansion of the replacement address, for example, to rewrite domains by file lookup.

• Whenever a domain list is being scanned, $domain contains the subject domain.

• When the smtp_etrn_command option is being expanded, $domain contains the complete argument of the ETRN command (see section 42.9).

$domain_data: When the domains option on a router matches a domain by means of a lookup, the data read by the lookup is available during the running of the router as $domain_data. In addition, if the driver routes the address to a transport, the value is available in that transport. If the transport is handling multiple addresses, the value from the first address is used.

$domain_data is also set when the domains condition in an ACL matches a domain by means of a lookup. The data read by the lookup is available during the rest of the ACL statement. In all other situations, this variable expands to nothing.

$header_<name>: This is not strictly an expansion variable. It is expansion syntax for inserting the message header line with the given name. Note that the name must be terminated by colon or white space, because it may contain a wide variety of characters. Note also that braces must not be used.

$home: When the check_local_user option is set for a router, the user's home directory is placed in $home when the check succeeds. In particular, this means it is set during the running of users' filter files. A router may also explicitly set a home directory for use by a transport; this can be overridden by a setting on the transport itself.

When running a filter test via the -bf option, $home is set to the value of the environment variable HOME.

$host: When the smtp transport is expanding its options for encryption using TLS, $host contains the name of the host to which it is connected. Likewise, when used in the client part of an authenticator configuration (see chapter 32), $host contains the name of the server to which the client is connected. When used in a transport filter (see chapter 23) $host refers to the host involved in the current connection. When a local transport is run as a result of a router that sets up a host list, $host contains the name of the first host.

$host_address: This variable is set to the remote host's IP address whenever $host is set for a remote connection.

  deny  hosts = net-lsearch;/some/file
        message = $host_data

$host_lookup_failed: This variable contains ``1'' if the message came from a remote host and there was an attempt to look up the host's name from its IP address, but the attempt failed. Otherwise the value of the variable is ``0''.

$inode: The only time this variable is set is while expanding the directory_file option in the appendfile transport. The variable contains the inode number of the temporary file which is about to be renamed. It can be used to construct a unique name for the file.

$interface_address: For a message received over a TCP/IP connection, this variable contains the address of the IP interface that was used. See also the -oMi command line option.

$interface_port: For a message received over a TCP/IP connection, this variable contains the port that was used. See also the -oMi command line option.

$ldap_dn: This variable, which is available only when Exim is compiled with LDAP support, contains the DN from the last entry in the most recently successful LDAP lookup.

$load_average: This variable contains the system load average, multiplied by 1000 to that it is an integer. For example, if the load average is 0.21, the value of the variable is 210. The value is recomputed every time the variable is referenced.

$local_part: When an address is being routed, or delivered on its own, this variable contains the local part. When a number of addresses are being delivered together (for example, multiple RCPT commands in an SMTP session), $local_part is not set.

Global address rewriting happens when a message is received, so the value of $local_part during routing and delivery is the value after rewriting. $local_part is set during user filtering, but not during system filtering, because a message may have many recipients and the system filter is called just once.

If a local part prefix or suffix has been recognized, it is not included in the value of $local_part during routing and subsequent delivery. The values of any prefix or suffix are in $local_part_prefix and $local_part_suffix, respectively.

When a message is being delivered to a file, pipe, or autoreply transport as a result of aliasing or forwarding, $local_part is set to the local part of the parent address, not to the file name or command (see $address_file and $address_pipe).

When an ACL is running for a RCPT command, $local_part contains the local part of the recipient address.

When a rewrite item is being processed (see chapter 30), $local_part contains the local part of the address that is being rewritten; it can be used in the expansion of the replacement address, for example.

In all cases, all quoting is removed from the local part. For example, for both the addresses

  "abc:xyz"@test.example
  abc\:xyz@test.example

the value of $local_part is

  abc:xyz

If you use $local_part to create another address, you should always wrap it inside a quoting operator. For example, in a redirect router you could have:

  data = ${quote:$local_part}@new.domain.example

$local_part_data: When the local_parts option on a router matches a local part by means of a lookup, the data read by the lookup is available during the running of the router as $local_part_data. In addition, if the driver routes the address to a transport, the value is available in that transport. If the transport is handling multiple addresses, the value from the first address is used.

$local_part_data is also set when the local_parts condition in an ACL matches a local part by means of a lookup. The data read by the lookup is available during the rest of the ACL statement. In all other situations, this variable expands to nothing.

$local_part_prefix: When an address is being routed or delivered, and a specific prefix for the local part was recognized, it is available in this variable, having been removed from $local_part.

$local_part_suffix: When an address is being routed or delivered, and a specific suffix for the local part was recognized, it is available in this variable, having been removed from $local_part.

$local_scan_data: This variable contains the text returned by the local_scan() function when a message is received. See chapter 38 for more details.

$localhost_number: This contains the expanded value of the localhost_number option. The expansion happens after the main options have been read.

$message_age: This variable is set at the start of a delivery attempt to contain the number of seconds since the message was received. It does not change during a single delivery attempt.

$message_body: This variable contains the initial portion of a message's body while it is being delivered, and is intended mainly for use in filter files. The maximum number of characters of the body that are put into the variable is set by the message_body_visible configuration option; the default is 500. Newlines are converted into spaces to make it easier to search for phrases that might be split over a line break. Binary zeros are also converted into spaces.

$message_body_end: This variable contains the final portion of a message's body while it is being delivered. The format and maximum size are as for $message_body.

$message_body_size: When a message is being processed, this variable contains the size of the body in bytes. The count starts from the character after the blank line that separates the body from the header. Newlines are included in the count. See also $message_size and $body_linecount.

$message_headers: This variable contains a concatenation of all the header lines when a message is being processed, except for lines added by routers or transports. The header lines are separated by newline characters.

$message_id: When a message is being received or delivered, this variable contains the unique message id that is used by Exim to identify the message. An id is not allocated to a message until after its header has been successfully received.

$message_size: When a message is being processed, this variable contains its size in bytes. In most cases, the size includes those headers that were received with the message, but not those (such as Envelope-to:) that are added to individual deliveries as they are written. However, there is one special case: during the expansion of the maildir_tag option in the appendfile transport while doing a delivery in maildir format, the value of $message_size is the precise size of the file that has been written. See also $message_body_size and $body_linecount.

While running an ACL at the time of an SMTP RCPT command, $message_size contains the size supplied on the MAIL command, or zero if no size was given. The value may not, of course, be truthful.

$n0 - $n9: These variables are counters that can be incremented by means of the add command in filter files.

$original_domain: When a top-level address is being processed for delivery, this contains the same value as $domain. However, if a ``child'' address (for example, generated by an alias, forward, or filter file) is being processed, this variable contains the domain of the original address. This differs from $parent_domain only when there is more than one level of aliasing or forwarding. When more than one address is being delivered in a single transport run, $original_domain is not set.

If new an address is created by means of a deliver command in a system filter, it is set up with an artificial ``parent'' address. This has the local part system-filter and the default qualify domain.

$original_local_part: When a top-level address is being processed for delivery, this contains the same value as $local_part, unless a prefix or suffix was removed from the local part, in which case $original_local_part contains the full local part. When a ``child'' address (for example, generated by an alias, forward, or filter file) is being processed, this variable contains the full local part of the original address. If the router that did the redirection processed the local part case-insensitively, the value in $original_local_part is in lower case. This variable differs from $parent_local_part only when there is more than one level of aliasing or forwarding. When more than one address is being delivered in a single transport run, $original_local_part is not set.

If new an address is created by means of a deliver command in a system filter, it is set up with an artificial ``parent'' address. This has the local part system-filter and the default qualify domain.

$originator_gid: The value of $caller_gid that was set when the message was received. For messages received via the command line, this is the gid of the sending user. For messages received by SMTP over TCP/IP, this is normally the gid of the Exim user.

$originator_uid: The value of $caller_uid that was set when the message was received. For messages received via the command line, this is the uid of the sending user. For messages received by SMTP over TCP/IP, this is normally the uid of the Exim user.

$parent_domain: This variable is similar to $original_domain (see above), except that it refers to the immediately preceding parent address.

$parent_local_part: This variable is similar to $original_local_part (see above), except that it refers to the immediately preceding parent address.

$pid: This variable contains the current process id.

$pipe_addresses: This is not an expansion variable, but is mentioned here because the string ``$pipe_addresses'' is handled specially in the command specification for the pipe transport (chapter 28) and in transport filters (described under transport_filter in chapter 23). It cannot be used in general expansion strings, and provokes an ``unknown variable'' error if encountered.

$primary_hostname: The value set in the configuration file, or read by the uname() function. If uname() returns a single-component name, Exim calls gethostbyname() (or getipnodebyname() where available) in an attempt to acquire a fully qualified host name.

$qualify_domain: The value set for this option in the configuration file.

$qualify_recipient: The value set for this option in the configuration file, or if not set, the value of $qualify_domain.

$rcpt_fail_count: When a message is being received by SMTP, this variable contains the number of RCPT commands in the current message that have previously been rejected with a permanent (5xx) response.

$received_for: If there is only a single recipient address in an incoming message, this variable contains that address when the Received: header line is being built.

$received_protocol: When a message is being processed, this variable contains the name of the protocol by which it was received. See also the -oMr option.

$recipients_count: When a message is being processed, this variable contains the number of envelope recipients that came with the message. Duplicates are not excluded from the count. While a message is being received over SMTP, the number increases for each accepted recipient. It can be referenced in an ACL.

$reply_address: When a message is being processed, this variable contains the contents of the Reply-To: header line if one exists and it is not empty, or otherwise the contents of the From: header line.

$return_path: When a message is being delivered, this variable contains the return path - the sender field that will be sent as part of the envelope. It is not enclosed in <> characters. In many cases, $return_path has the same value as $sender_address, but if, for example, an incoming message to a mailing list has been expanded by a router which specifies a different address for bounce messages, $return_path contains the new bounce address, whereas $sender_address contains the original sender address that was received with the message.

$return_size_limit: This contains the value set in the return_size_limit option, rounded up to a multiple of 1000. It is useful when a customized error message text file is in use (see chapter 40).

$runrc: This variable contains the return code from a command that is run by the ${run...} expansion item. Warning: In a router or transport, you cannot assume the order in which option values are expanded, except for those pre-conditions whose order of testing is documented. Therefore, you cannot reliably expect to set $runrc by the expansion of one option, and use it in another.

$self_hostname: When an address is routed to a supposedly remote host that turns out to be the local host, what happens is controlled by the self generic router option. One of its values causes the address to be passed to another router. When this happens, $self_hostname is set to the name of the local host that the original router encountered. In other circumstances its contents are null.

$sender_address: When a message is being processed, this variable contains the sender's address that was received in the message's envelope. For bounce messages, the value of this variable is the empty string.

$sender_address_domain: The domain portion of $sender_address.

$sender_address_local_part: The local part portion of $sender_address.

$sender_fullhost: When a message is received from a remote host, this variable contains the host name and IP address in a single string. It ends with the IP address in square brackets, followed by a colon and a port number if the logging of ports is enabled. The format of the rest of the string depends on whether the host issued a HELO or EHLO SMTP command, and whether the host name was verified by looking up its IP address. (Looking up the IP address can be forced by the host_lookup option, independent of verification.) A plain host name at the start of the string is a verified host name; if this is not present, verification either failed or was not requested. A host name in parentheses is the argument of a HELO or EHLO command. This is omitted if it is identical to the verified host name or to the host's IP address in square brackets.

$sender_helo_name: When a message is received from a remote host that has issued a HELO or EHLO command, the argument of that command is placed in this variable. It is also set if HELO or EHLO is used when a message is received using SMTP locally via the -bs or -bS options.

$sender_host_address: When a message is received from a remote host, this variable contains that host's IP address. For locally submitted messages, it is empty.

$sender_host_authenticated: This variable contains the name (not the public name) of the authenticator driver which successfully authenticated the client from which the message was received. It is empty if there was no successful authentication.

$sender_host_name: When a message is received from a remote host, this variable contains the host's name as obtained by looking up its IP address. If the lookup failed, or was not requested, this variable contains the empty string.

Exim does not always look up every calling host's name. If you want maximum efficiency, you should arrange your configuration so that it avoids these lookups altogether. The lookup happens only if any of the following are true:

1. The calling host matches the list in host_lookup. The default for this option is *, so it must be changed if any lookups are to be avoided.

2. Exim needs the host name in order to test an item in a host list. The items that require this are described in section 10.11. A common mistake is to forget to use ``net-'' before a query-style lookup that actually looks up the host address.

3. The calling host matches helo_try_verify_hosts or helo_verify_hosts. In this case, the host name is required to compare with the name quoted in any EHLO or HELO commands that the client issues.

4. The remote host issues a EHLO or HELO command that quotes one of the domains in helo_lookup_domains. The default value of this option is

     helo_lookup_domains = @ : @[]
   

   which causes a lookup if a remote host (incorrectly) gives the server's name or IP address in an EHLO or HELO command.

$sender_host_port: When a message is received from a remote host, this variable contains the port number that was used on the remote host.

$sender_ident: When a message is received from a remote host, this variable contains the identification received in response to an RFC 1413 request. When a message has been received locally, this variable contains the login name of the user that called Exim.

$sender_rcvhost: This is provided specifically for use in Received: headers. It starts with either the verified host name (as obtained from a reverse DNS lookup) or, if there is no verified host name, the IP address in square brackets. After that there may be text in parentheses. When the first item is a verified host name, the first thing in the parentheses is the IP address in square brackets, followed by a colon and a port number if port logging is enabled. When the first item is an IP address, the port is recorded as ``port=xxxx'' inside the parentheses.

There may also be items of the form ``helo=xxxx'' if HELO or EHLO was used and its argument was not identical to the real host name or IP address, and ``ident=xxxx'' if an RFC 1413 ident string is available. If all three items are present in the parentheses, a newline and tab are inserted into the string, to improve the formatting of the Received: header.

$smtp_command_argument: While an ACL is running to check an AUTH, EHLO, EXPN, ETRN, HELO, or VRFY command, this variable contains the argument for the SMTP command.

$sn0 - $sn9: These variables are copies of the values of the $n0 - $n9 accumulators that were current at the end of the system filter file. This allows a system filter file to set values that can be tested in users' filter files. For example, a system filter could set a value indicating how likely it is that a message is junk mail.

$spool_directory: The name of Exim's spool directory.

$thisaddress: This variable is set only during the processing of the foranyaddress command in a filter file. Its use is explained in the description of that command.

$tls_certificate_verified: This variable is set to ``1'' if a TLS certificate was verified when the message was received, and ``0'' otherwise.

$tls_cipher: When a message is received from a remote host over an encrypted SMTP connection, this variable is set to the cipher suite that was negotiated, for example DES-CBC3-SHA. In other circumstances, in particular, for message received over unencrypted connections, the variable is empty. See chapter 36 for details of TLS support.

$tls_peerdn: When a message is received from a remote host over an encrypted SMTP connection, and Exim is configured to request and verify a certificate from the client, the value of the Distinguished Name of the certificate is made available in the $tls_peerdn during subsequent processing.

$tod_bsdinbox: The time of day and date, in the format required for BSD-style mailbox files, for example: Thu Oct 17 17:14:09 1995.

$tod_epoch: The time and date as a number of seconds since the start of the Unix epoch.

$tod_full: A full version of the time and date, for example: Wed, 16 Oct 1995 09:51:40 +0100. The timezone is always given as a numerical offset from UTC, with positive values used for timezones that are ahead (east) of UTC, and negative values for those that are behind (west).

$tod_log: The time and date in the format used for writing Exim's log files, for example: 1995-10-12 15:32:29, but without a timezone.

$tod_zulu: This variable contains the UTC date and time in ``Zulu'' format, as specified by ISO 8601, for example: 20030221154023Z.

$value: This variable contains the result of an expansion lookup, extraction operation, or external command, as described above.

$version_number: The version number of Exim.

$warn_message_delay: This variable is set only during the creation of a message warning about a delivery delay. Details of its use are explained in section 40.2.

$warn_message_recipients: This variable is set only during the creation of a message warning about a delivery delay. Details of its use are explained in section 40.2.