The following generic options apply to all transports:
If this option is set, the message's headers are not transported. It is mutually exclusive with headers_only. If it is used with the appendfile or pipe transports, the settings of message_prefix and message_suffix should be checked, because this option does not automatically suppress them.
This specifies the current directory that is to be set while running the
transport, overriding any value that may have been set by the router.
If this option is set true, nothing is logged for any transport errors. You should not set this option unless you really, really know what you are doing.
If this option is set and debugging is enabled (see the -d command line option), the string is expanded and included in the debugging output when the transport is run. This is to help with checking out the values of variables and so on when debugging driver configurations. For example, if a headers_add option is not working properly, debug_print could be used to output the variables it references. A newline is added to the text if it does not end with one.
If this option is true, a Delivery-date: header is added to the message. This gives the actual time the delivery was made. As this is not a standard header, Exim has a configuration option (delivery_date_remove) which requests its removal from incoming messages, so that delivered messages can safely be resent to other recipients.
This specifies which of the available transport drivers is to be used. There is no default, and this option must be set for every transport.
If this option is true, an Envelope-to: header is added to the message. This gives the original address(es) in the incoming envelope that caused this delivery to happen. More than one address may be present if the transport is configured to handle several addresses at once, or if more than one original address was redirected to the same final address. As this is not a standard header, Exim has a configuration option (envelope_to_remove) which requests its removal from incoming messages, so that delivered messages can safely be resent to other recipients.
This option specifies a gid for running the transport process, overriding any value that the router supplies, and also overriding any value associated with user (see below).
This option specifies a string of text which is expanded and added to the header portion of a message as it is transported. If the result of the expansion is an empty string, or if the expansion is forced to fail, no action is taken. Other expansion failures are treated as errors and cause the delivery to be deferred. The expanded string should be in the form of one or more RFC 2822 header lines, separated by newlines (coded as ``\n''), for example:
headers_add = X-added: this is a header added at $tod_log\n\ X-added: this is another
Exim does not check the syntax of these added headers. A newline is supplied at the end if one is not present. The text is added at the end of any existing headers. If you include a blank line within the string, you can subvert this facility into adding text at the start of the message's body. This is not recommended. Additional headers can also be specified by routers. See chapter 14 and section 43.13.
If this option is set, the message's body is not transported. It is mutually exclusive with body_only. If it is used with the appendfile or pipe transports, the settings of message_prefix and message_suffix should be checked, since this option does not automatically suppress them.
This option is expanded; the result must consist of a colon-separated list of header names, not including the terminating colon, for example:
headers_remove = return-receipt-to:acknowledge-to
Any existing headers matching those names are not included in any message that is transmitted by the transport. If there are multiple instances of a header, they are all removed. However, added headers may have these names. Thus it is possible to replace a header by specifying it in headers_remove and supplying the replacement in headers_add. Headers to be removed can also be specified by routers. See chapter 14 and section 43.13.
This option allows addresses in header lines to be rewritten at transport time, that is, as the message is being copied to its destination. The contents of the option are a colon-separated list of rewriting rules. Each rule is in exactly the same form as one of the general rewriting rules that are applied when a message is received. These are described in chapter 30. For example,
headers_rewrite = a@b c@d f : \ x@y w@z
changes a@b into c@d in From: header lines, and x@y into w@z in all address-bearing header lines. The rules are applied to the header lines just before they are written out at transport time, so they affect only those copies of the message that pass through the transport. However, only the message's original header lines, and any that were added by a system filter, are rewritten. If a router or transport adds header lines, they are not affected by this option. These rewriting rules are not applied to the envelope. You can change the return path using return_path, but you cannot change envelope recipients at this time.
This option specifies a home directory setting for the transport, overriding any value that may be set by the router. The home directory is placed in $home while expanding the transport's private options. It is also used as the current directory if no current directory is set by the current_directory option on the transport or the transport_current_directory option on the router.
If this option is true and the uid for the delivery process is provided by the transport, the initgroups() function is called when running the transport to ensure that any additional groups associated with the uid are set up.
This option controls the size of messages passed through the transport. It is expanded before use; any expansion failure causes delivery to be deferred. The result of the expansion must be a sequence of digits, optionally followed by K or M. If its value is greater than zero and the size of a message exceeds the limit, the address is failed. If there is any chance that the resulting bounce message could be routed to the same transport, you should ensure that return_size_limit is less than the transport's message_size_limit, as otherwise the bounce message will fail to get delivered.
When a delivery suffers a temporary failure, a retry record is created in Exim's hints database. For remote deliveries, the key for the retry record is based on the name and/or IP address of the failing remote host. For local deliveries, the key is normally the entire address, including both the local part and the domain. This is suitable for most common cases of local delivery temporary failure - for example, exceeding a mailbox quota should delay only deliveries to that mailbox, not to the whole domain.
However, in some special cases you may want to treat a temporary local delivery as a failure associated with the domain, and not with a particular local part. (For example, if you are storing all mail for some domain in files.) You can do this by setting retry_use_local_part false.
For all the local transports, its default value is true. For remote transports, the default value is false for tidiness, but changing the value has no effect on a remote transport in the current implementation.
If this option is set, the string is expanded at transport time and replaces the existing return path (envelope sender) value in the copy of the message that is being delivered. An empty return path is permitted. This feature is designed for remote deliveries, where the value of this option is used in the SMTP MAIL command. If you set return_path for a local transport, the only effect is to change the address that is placed in the Return-path: header line, if one is added to the message (see the next option).
The expansion can refer to the existing value via $return_path. This is either the message's envelope sender, or an address set by the errors_address option on a router. If the expansion is forced to fail, no replacement occurs; if it fails for another reason, delivery is deferred. This option can be used to support VERP (Variable Envelope Return Paths) - see chapter 42.
Note: If a delivery error is detected locally, the bounce message is not sent to the value of this option, but to the previously set errors address.
If this option is true, a Return-path: header is added to the message. Although the return path is normally available in the prefix line of BSD mailboxes, this is commonly not displayed by MUAs, and so the user does not have easy access to it.
RFC 2821 states that the Return-path: header is added to a message ``when the delivery SMTP server makes the final delivery''. This implies that this header should not be present in incoming messages. Exim has a configuration option, return_path_remove, which requests removal of this header from incoming messages, so that delivered messages can safely be resent to other recipients.
See shadow_transport below.
A local transport may set the shadow_transport option to the name of another local transport. Shadow remote transports are not supported.
Whenever a delivery to the main transport succeeds, and either shadow_condition is unset, or its expansion does not result in a forced expansion failure or the empty string or one of the strings ``0'' or ``no'' or ``false'', the message is also passed to the shadow transport, with the same delivery address or addresses. However, the result of the shadow transport is discarded and does not affect the subsequent processing of the message. Only a single level of shadowing is provided; the shadow_transport option is ignored on any transport when it is running as a shadow. Options concerned with output from pipes are also ignored.
The log line for the successful delivery has an item added on the end, of the form
ST=<shadow transport name>
If the shadow transport did not succeed, the error message is put in parentheses afterwards.
Shadow transports can be used for a number of different purposes, including keeping more detailed log information than Exim normally provides, and implementing automatic acknowledgement policies based on message headers that some sites insist on.
This option sets up a filtering (in the Unix shell sense) process for messages at transport time. It should not be confused with mail filtering as set up by individual users or via a system filter.
When the message is about to be written out, the command specified by transport_filter is started up in a separate process, and the entire message, including the header lines, is passed to it on its standard input (this in fact is done from a third process, to avoid deadlock). The command must be specified as an absolute path.
The message is passed to the filter before any SMTP-specific processing, such as turning ``\n'' into ``\r\n'' and escaping lines beginning with a dot, and also before any processing implied by the settings of check_string and escape_string in the appendfile or pipe transports.
The filter's standard output is read and written to the message's destination. The filter can perform any transformations it likes, but of course should take care not to break RFC 2822 syntax. A demonstration Perl script is provided in util/transport-filter.pl; this makes a few arbitrary modifications just to show the possibilities. Exim does not check the result, except to test for a final newline when SMTP is in use. All messages transmitted over SMTP must end with a newline, so Exim supplies one if it is missing.
A problem might arise if the filter increases the size of a message that is being sent down an SMTP connection. If the receiving SMTP server has indicated support for the SIZE parameter, Exim will have sent the size of the message at the start of the SMTP session. If what is actually sent is substantially more, the server might reject the message. This can be worked round by setting the size_addition option on the smtp transport, either to allow for additions to the message, or to disable the use of SIZE altogether.
The value of the option is the command string for starting up the filter, which is run directly from Exim, not under a shell. The string is parsed by Exim in the same way as a command string for the pipe transport: Exim breaks it up into arguments and then expands each argument separately. The special argument $pipe_addresses is replaced by a number of arguments, one for each address that applies to this delivery. (This isn't an ideal name for this feature here, but as it was already implemented for the pipe transport, it seemed sensible not to change it.)
The expansion variables $host and $host_address are available when the transport is a remote one. They contain the name and IP address of the host to which the message is being sent. For example:
transport_filter = /some/directory/transport-filter.pl \ $host $host_address $sender_address $pipe_addresses
The filter process is run under the same uid and gid as the normal delivery. For remote deliveries this is the Exim uid/gid by default.
If a transport filter is set on an autoreply transport, the original message is passed through the filter as it is being copied into the newly generated message, which happens if the return_message option is set.
This option specifies the user under whose uid the delivery process is to be run, overriding any uid that may have been set by the router. If the user is given as a name, the uid is looked up from the password data, and the associated group is taken as the value of the gid to be used if the group option is not set.
For remote transports, you should leave this option unset unless you really are sure you know what you are doing. When a remote transport is running, it needs to be able to access Exim's hints databases, because each host may have its own retry data.