Mailbox

A mailbox is a file on a mail server that is the final destination for email messages. The name of the mailbox may 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 may 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.
x-interest	Names with dashes are likely to be a distribution list or a mailing list. This format is commonly used for net mail groups.
x-interest-request	Names ending in -request are administrative addresses for distribution lists.
owner-x-interest	Names beginning with owner- are administrative addresses for distribution lists.
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."