The default configuration file

The default configuration file supplied with Exim as `src/configure.default' is sufficient for a single host with simple mail requirements. It contains comments about options you might want to set, but which it lets default, together with the settings described here.

Main configuration settings

There are two explicit options in this section:

never_users = root

This prevents Exim from ever running as root when performing a local delivery. Instead, it runs as `nobody'.

host_lookup = 0.0.0.0/0

This specifies the sending IP networks for which a DNS reverse lookup is done, in order to get the host name from the IP address of an incoming message. The default setting matches all IP addresses. The host name appears in the log and in messages' `Received:' headers.

As the `primary_hostname', `qualify_domain', and `local_domains' options are not specified, they all take the name of the local host, as obtained by the `uname()' function, as their value.

No relaying is permitted through the host, because neither `relay_domains' nor `host_accept_relay' is set. See chapter "Other policy controls on incoming mail" for more details about relay control.

Transport configuration settings

remote_smtp:
  driver = smtp

This transport is used to do external deliveries over SMTP, with default options. The first local transport is

local_delivery:
  driver = appendfile
  file = /var/mail/${local_part}
  delivery_date_add
  envelope_to_add
  return_path_add

This is set up to deliver to local mailboxes in a traditional `sticky bit' directory. Some installations prefer not to set the `sticky bit', but instead run the delivery under a specific group, with the directory being writeable by the group. Adding the following options achieves this:

   group = mail
   mode = 0660

To deliver into files in users' home directories, a setting such as

  file = /home/${local_part}/inbox

or

  file = ${home}/inbox

should be substituted for the default `file' option. The three options ending in `_add' cause Exim to add three header lines to the message as it writes it to the mailbox. They can be removed if these headers are not required. The second local transport is

address_pipe:
  driver = pipe
  return_output

This transport is used by Exim when a local part that is expanded via an alias or forward file causes delivery to a pipe. Any output from the pipe is returned to the sender of the message. The third local transport is

address_file:
  driver = appendfile
  delivery_date_add
  envelope_to_add
  return_path_add

This transport is used by Exim when a local part that is expanded via an alias or forward file causes delivery to a specified file (by generating a path name not ending in `/'). The final local transport is

address_reply:
  driver = autoreply

This transport used by Exim when a local part that is expanded via a filter file causes an automatic reply to a message to be generated.

Director configuration settings

Three directors are specified for the default configuration. Note that the order of director definitions matters. The first director causes local parts to be checked against the system alias file, which is searched linearly:

system_aliases:
  driver = aliasfile
  file = /etc/aliases
  search_type = lsearch
  file_transport = address_file
  pipe_transport = address_pipe

If an alias generates a file or pipe delivery, the `address_file' or `address_pipe' transport is used, as appropriate. The second director comes into play if a local part does not match a system alias:

userforward:
  driver = forwardfile
  file = .forward
  no_verify
  no_expn
  check_ancestor
# filter
  file_transport = address_file
  pipe_transport = address_pipe
  reply_transport = address_reply

An attempt is made to look for a file called `.forward' in the home directory of a local user. However, this director is skipped when verifying addresses or running an SMTP EXPN command. The `check_ancestor' option prevents a `.forward' file from turning a login name back into a previously-handled alias name. The `filter' option is commented out in the default configuration. Thus `.forward' files are treated in the conventional manner, but filtering can be enabled by removing the # character.

If forwarding or filtering generates a file, pipe, or autoreply delivery, the `address_file', `address_pipe', or `address_reply' transport is used, as appropriate. The final director is

localuser:
  driver = localuser
  transport = local_delivery

This checks that a local part is the login of a local user, and if so, directs the message to be delivered using the `local_delivery' transport.

Router configuration settings

Two routers are defined in the default configuration. The first is

lookuphost:
  driver = lookuphost
  transport = remote_smtp

and its default settings cause it to look up the domain in the DNS, in order to determine the host to which a message should be sent, using the `remote_smtp' transport. The second router is

literal:
  driver = ipliteral
  transport = remote_smtp

This handles `domains' that are actually RFC 822 domain literals, that is, IP addresses enclosed in square brackets.

Default retry rule

A single retry rule is given in the default configuration:

*    *   F,2h,15m; G,16h,1h,1.5; F,4d,8h

This causes any temporarily failing address to be retried every 15 minutes for 2 hours, then at intervals starting at one hour and increasing by a factor of 1.5 until 16 hours have passed, then every 8 hours up to 4 days.

Rewriting configuration

There are no rewriting rules in the default configuration file.

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