A local address most commonly denotes a user's mailbox. This is normally located in /var/spool/mail and has the name of the user, who also owns the file. If it does not exist, it is created by Exim.
In some configurations, the group is set to the user's group and the mode is 0600. In these cases, delivery processes are run as the user, and the user may delete the mailbox entirely. In other configurations, the mailbox's group is mail, and it has mode 660; delivery processes are run under a system uid and group mail, and users cannot delete their mailbox files, though they can empty them.
Note that although /var/spool/mail is currently the standard place to put the mailbox files, some mail software may be compiled to use different paths, for example, /usr/spool/mail. If delivery to users on your machine fails consistently, you should see if it helps to make this a symbolic link to /var/spool/mail.
The addresses MAILER-DAEMON and postmaster should normally appear in your alias file, expanding into the email address of the system administrator. MAILER-DAEMON is used by Exim as the sender address in bounce messages. It is also recommended that root be set up as an alias for an administrator, especially when deliveries are being run under the permissions of the recipient users, in order to avoid running any delivery as root.
Users can redirect their mail to alternative addresses by creating a .forward file in their home directories. This contains a list of recipients separated by commas and/or newlines. All lines of the file are read and interpreted. Any type of address may be used. A practical example of a .forward file for vacations might be:
janet, '|vacation'
In other descriptions of .forward files, you might see the username at the start preceded by a backslash. This was necessary in some older MTAs to stop a search for a .forward for the new name, which could lead to looping. The backslash is not necessary in Exim, which automatically avoids loops of this kind.[119] However, a backslash is permitted, and in fact it does make a difference in configurations where several domains are being handled at once. Without a backslash, an unqualified username is qualified with a default domain; with a backslash the incoming domain is preserved.
The first address in the forward file delivers the incoming message to janet's mailbox, while the vacation command returns a short notification to the sender.[120]
In addition to supporting 'traditional' forwarding files, Exim can be configured to allow more complex files called filters. Instead of being just a list of forwarding addresses, a filter file can contain tests on the contents of the incoming message so that, for example, messages could be forwarded only if the subject contained the message 'urgent.' The system administrator must decide whether to allow users this flexibility.
Exim is able to handle alias files compatible with Berkeley's sendmail alias files. Entries in the alias file can have the following form:
alias: recipients
recipients is a comma-separated list of addresses that will be substituted for the alias. The recipient list may be continued across newlines if the next line begins with whitespace.
A special feature allows Exim to handle mailing lists that are held separately from the alias file: if you specify:include: filename as a recipient, Exim reads the specified file and substitutes its contents as a list of recipients. An alternative to handling mailing lists is shown later in this chapter in 'Mailing Lists'.
The main aliases file is /etc/aliases. If you make this file world-writable or group-writeable, Exim will refuse to use it and will defer local deliveries. You can control the test it applies to the file's permissions by setting modemask in the system_aliases director.
This is a sample aliases file:
# vbrew.com /etc/aliases file
hostmaster: janet
postmaster: janet
usenet: phil
# The development mailing list.
development: joe, sue, mark, biff,
/var/mail/log/development
owner-development: joe
# Announcements of general interest are mailed to all
# of the staff
announce::include: /etc/Exim/staff,
/var/mail/log/announce
owner-announce: root
# gate the ppp mailing list to a local newsgroup
ppp-list: '|/usr/local/bin/gateit local.lists.ppp'
When there are file names and pipe commands in an alias file, as here, Exim needs to be told which userid to run the deliveries under. The user option (and possibly group, too) must be set in Exim's configuration file, either on the director that is handling the aliases, or on the transports to which it directs these items.
If an error occurs while delivering to an address generated from the aliases file, Exim will send a bounce message to the sender of the message, as usual, but this might not be appropriate. The errors_to option can be used to specify that bounce messages are to be sent elsewhere; for example, to the postmaster.
Instead of the aliases file, mailing lists may also be managed by means a forwardfile director. The lists are all kept in a single directory such as /etc/exim/lists/, and a mailing list named nag-bugs is described by the file lists/nag-bugs. This should contain the members' addresses separated by commas or newlines. Lines beginning with a hash sign (#) are treated as comments. A simple
