mailaddr — mail addressing description


This manual page gives a brief introduction to SMTP mail addresses, as used on the Internet. These addresses are in the general format

[email protected]

where a domain is a hierarchical dot-separated list of subdomains. These examples are valid forms of the same address:

[email protected]

John Doe <[email protected]>

[email protected] (John Doe)

The domain part ("") 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.

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:


USER%[email protected]

[email protected]

[email protected]

(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.)

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 ".":

"John Q. Doe" <[email protected]>


Some mail systems let users abbreviate the domain name. For instance, users at may get away with "[email protected]" to send mail to John Doe. This behavior is deprecated. Sometimes it works, but you should not depend on it.


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:

<@hosta,@hostb:[email protected]>

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.

Route-addrs are very unusual now. They occur sometimes in old mail archives. It is generally possible to ignore all but the "[email protected]" part of the address to determine the actual address.


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.





mail(1), aliases(5), forward(5), sendmail(8)



This page is part of release 4.16 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at−pages/.

  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 <>.  My
changes are placed under the same copyright as the original BSD page.

Adjusted by Arnt Gulbrandsen <> in 2004 to
account for changes since 1995. Route-addrs are now even less
common, etc. Some minor wording improvements. Same copyright.

Redistribution and use in source and binary forms are permitted
provided that the above copyright notice and this paragraph are
duplicated in all such forms and that any documentation,
advertising materials, and other materials related to such
distribution and use acknowledge that the software was developed
by the University of California, Berkeley.  The name of the
University may not be used to endorse or promote products derived
from this software without specific prior written permission.