Mail Administration Guide

Mailbox

A mailbox is a file on a mail server that is the final destination for email messages. The name of the mailbox can be the user name or a place to put mail for someone with a specific function, like the postmaster. Mailboxes are in the /var/mail/username file, which can exist either on the user's local system or on a remote mail server. In either case, the mailbox is on the system to which the mail is delivered.

Mail should always be delivered to a local file system so that the user agent can pull mail from the mail spool and store it readily in the local mailbox. Do not use NFS-mounted file systems as the destination for a user's mailbox. Specifically, do not direct mail to a mail client that is mounting the /var/mail file system from a remote server. Mail for the user, in this case, should be addressed to the mail server and not to the client host name. NFS-mounted file systems can cause problems with mail delivery and handling. Clients that NFS-mount /var/mail go into "remote mode" and should arrange to have the server send and receive mail for them.

The /etc/mail/aliases file and name services like NIS and NIS+ provide mechanisms for creating aliases for electronic mail addresses, so that users do not need to know the precise local name of a user's mailbox.

Table 1-2 shows some common naming conventions for special-purpose mailboxes.

Table 1-2 Conventions for the Format of Mailbox Names


Format	Description
`username`	User names are frequently the same as mailbox names.
`Firstname.Lastname` `Firstname_Lastname` `Firstinitial.Lastname` `Firstinitial_Lastname`	User names can be identified as full names with a dot (or an underscore) separating the first and last names, or by a first initial with a dot (or an underscore) separating the initial and the last name.
`postmaster`	Users can address questions and report problems with the mail system to the `postmaster` mailbox. Each site and domain should have a `postmaster` mailbox.
`MAILER-DAEMON`	`sendmail` automatically routes any mail addressed to the `MAILER-DAEMON` to the postmaster.
`aliasname-request`	Names ending in `-request` are administrative addresses for distribution lists. This address should redirect mail to the person who maintains the distribution list.
`owner-aliasname`	Names beginning with `owner-` are administrative addresses for distribution lists. This address should redirect mail to the person who handles mail errors.
`owner-owner`	This alias is used when there is no `owner-aliasname` alias for errors to be returned to. This address should redirect mail to the person who handles mail errors and should be defined on any system that maintains a large number of aliases.
`local%domain`	The percent sign (`%`) marks a local address that is expanded when the message arrives at its destination. Most mail systems interpret mailbox names with `%` characters as full mail addresses. The `%` is replaced with an `@`, and the mail is redirected accordingly. Although many people use the `%` convention, it is not a formal standard. It is referred to as the "percent hack." This feature is often used to help debug mail problems.

Starting with version 8, the envelop sender for mail sent to an group alias is changed to the address expanded from the owner alias, if an owner alias exists. This change allows for any mail errors to be sent to the alias owner rather than being returned to the sender. What users will notice is that mail they send to an alias, when delivered, will look like it came from the alias owner. The following alias format will help with some of the problems associated with this change:

mygroup: :include:/pathname/mygroup.list
owner-mygroup: mygroup-request
mygroup-request: sandys, ignatz

In this example, the mygroup alias is the actual mail alias for the group; the owner-mygroup alias receives error messages; and the mygroup-request alias should be used for administrative requests. This structure means that in mail sent to the mygroup alias, the envelope sender changes to mygroup-request.