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
where a domain is a hierarchical dot-separated list of subdomains. These
examples are valid forms of the same address:
John Doe <email@example.com>
firstname.lastname@example.org (John Doe)
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.
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
(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@example.com>
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. 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:
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
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.
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.
This page is part of release 4.16 of the Linux man-pages
description of the project, information about reporting bugs, and the latest
version of this page, can be found at