.\" Copyright (c) 1983, 1987 The Regents of the University of California.
.\" All rights reserved.
.\"
.\"	@(#)mailaddr.7	6.5 (Berkeley) 2/14/89
.\"
.\" Extensively rewritten by Arnt Gulbrandsen <agulbra@troll.no>.  My
.\" changes are placed under the same copyright as the original BSD page.
.\"
.\" Adjusted by Arnt Gulbrandsen <arnt@gulbrandsen.priv.no> in 2004 to
.\" account for changes since 1995. Route-addrs are now even less
.\" common, etc. Some minor wording improvements. Same copyright.
.\"
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.\"
.TH mailaddr 7 2023-02-05 "Linux man-pages 6.04"
.UC 5
.SH NAME
mailaddr \- mail addressing description
.SH DESCRIPTION
.nh
This manual page gives a brief introduction to SMTP mail addresses,
as used on the Internet.
These addresses are in the general format
.PP
.in +4n
.EX
user@domain
.EE
.in
.PP
where a domain is a hierarchical dot-separated list of subdomains.
These examples are valid forms of the same address:
.PP
.in +4n
.EX
john.doe@monet.example.com
John Doe <john.doe@monet.example.com>
john.doe@monet.example.com (John Doe)
.EE
.in
.PP
The domain part ("monet.example.com") is a mail-accepting domain.
It can be a host and in the past it usually was, but it doesn't have to be.
The domain part is not case sensitive.
.PP
The local part ("john.doe") is often a username,
but its meaning is defined by the local software.
Sometimes it is case sensitive,
although that is unusual.
If you see a local-part that looks like garbage,
it is usually because of a gateway between an internal e-mail
system and the net, here are some examples:
.PP
.in +4n
.EX
"surname/admd=telemail/c=us/o=hp/prmd=hp"@some.where
USER%SOMETHING@some.where
machine!machine!name@some.where
I2461572@some.where
.EE
.in
.PP
(These are, respectively, an X.400 gateway, a gateway to an arbitrary
internal mail system that lacks proper internet support, an UUCP
gateway, and the last one is just boring username policy.)
.PP
The real-name part ("John Doe") can either be placed before
<>, or in () at the end.
(Strictly speaking the two aren't the same,
but the difference is beyond the scope of this page.)
The name may have to be quoted using "", for example, if it contains ".":
.PP
.in +4n
.EX
"John Q. Doe" <john.doe@monet.example.com>
.EE
.in
.SS Abbreviation
Some mail systems let users abbreviate the domain name.
For instance,
users at example.com may get away with "john.doe@monet" to
send mail to John Doe.
.I This behavior is deprecated.
Sometimes it works, but you should not depend on it.
.SS Route-addrs
In the past, sometimes one had to route a message through
several hosts to get it to its final destination.
Addresses which show these relays are termed "route-addrs".
These use the syntax:
.PP
.in +4n
.EX
<@hosta,@hostb:user@hostc>
.EE
.in
.PP
This specifies that the message should be sent to hosta,
from there to hostb, and finally to hostc.
Many hosts disregard route-addrs and send directly to hostc.
.PP
Route-addrs are very unusual now.
They occur sometimes in old mail archives.
It is generally possible to ignore all but the "user@hostc"
part of the address to determine the actual address.
.SS Postmaster
Every site is required to have a user or user alias designated
"postmaster" to which problems with the mail system may be
addressed.
The "postmaster" address is not case sensitive.
.SH FILES
.I /etc/aliases
.br
.I \[ti]/.forward
.SH SEE ALSO
.BR mail (1),
.BR aliases (5),
.BR forward (5),
.BR sendmail (8)
.PP
.UR http://www.ietf.org\:/rfc\:/rfc5322.txt
IETF RFC\ 5322
.UE