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. For example, the addresses

Eric Allman <> (Eric Allman)

are valid forms of the same address.

The domain part (‘‘’’) may be the name of an internet host, or it may be a logical mail address. 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. It can be case sensitive, but usually isn’t. 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 inernal 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 first, outside <>, or last, inside (). (Strictly speaking the two aren’t the same, but the difference is outside the scope of this page.) The name may have to be quoted using "" if it contains certain characters, most commonly ‘‘.’’:

"Eric P. Allman" <>


Many mail systems let users abbreviate the domain name. For instance, users at may get away with ‘‘eric@monet’’ to send mail to Eric Allman. This behavior is deprecated.


Under some circumstances it may be necessary to route a message through several hosts to get it to the final destination. Normally this happens automatically and invisibly, but sometimes not, particularly with old and broken software. 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. Some hosts disregard route-addrs and send directly to hostc.

Route-addrs occur frequently on return addresses, since these are generally augmented by the software at each host. It is generally possible to ignore all but the ‘‘user@hostc’’ part of the address to determine the actual sender.


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.

FREQUENTLY ASKED QUESTIONS and many mirrors store a collection of FAQs. Please find and use a nearby FAQ archive; there are dozens or hundreds around the world. mail/inter-network-guide explains how to send mail between many different networks. mail/country-codes lists the top level domains (e.g. ‘‘no’’ is Norway and ‘‘ea’’ is Eritrea). mail/college-email/part* gives some useful tips on how to locate e-mail addresses.




binmail(1), mail(1), mconnect(1), forward(5), aliases(5), sendmail(8), vrfy(8), RFC822 (Standard for the Format of Arpa Internet Text Messages).