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.
There are three 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.
forbid_domain_literals
This locks out the use of `domain literal' addresses such as
root@[192.168.35.43]
at the syntactic level. Although still specified in the RFCs, such addresses are not of great relevance in today's Internet, are not understood by many people, and have been abused by spammers seeking open relays.
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.
Four local transports and one remote transport are defined. The first one is the remote transport:
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 is used by Exim when a local part that is expanded via a filter file causes an automatic reply to a message to be generated.
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.
Only one router is defined in the default configuration:
lookuphost: driver = lookuphost transport = remote_smtp
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.
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.
There are no rewriting rules in the default configuration file.
No authenticators are specified in the default configuration file. Note that in order to use SMTP authentication, it is necessary to specify at least one authenticator in `Local/Makefile'.
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