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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:
Eric Allman <email@example.com>
firstname.lastname@example.org (Eric Allman)
The domain part ("monet.berkeley.edu") 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 ("eric") is often a user name, 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:
(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 ("Eric Allman") 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 "", e.g. if it contains ".":
"Eric P. Allman" <email@example.com>
Many mail systems let users abbreviate the domain name. For instance,
users at berkeley.edu may get away with "eric@monet" to send mail to
Eric Allman. This behavior is deprecated. Sometimes it works, but you
should not depend on it.
In the past, sometimes one had to route 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 hostc.
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.
binmail(1), mail(1), mconnect(1), aliases(5), forward(5), sendmail(8),
RFC 2822 (Internet Message Format)