mailaddr
—
mail addressing description
Mail addresses are based on the Internet protocol listed at the end of this
manual page. These addresses are in the general format
user@domain
where a domain is a hierarchical dot separated list of subdomains.
For example, a valid address is:
eric@CS.Berkeley.EDU
Unlike some other (now obsolete) forms of addressing, domains do
not imply any routing, or the existence of a particular host. Simply because
mail may be sent to ``user@somedomain.com'' does not imply that there is any
actual host named ``somedomain.com'', and does not imply a particular
routing of the message. Routing is performed by Mail Transport Agents, such
as postfix(1), based on
policies set in the MTA's configuration.
Under certain circumstances it may not be necessary to type the entire domain
name. In general, anything following the first dot may be omitted if it is the
same as the domain from which you are sending the message. For example, a user
on ``calder.berkeley.edu'' could send to ``eric@CS'' without adding the
``berkeley.edu'' since it is the same on both sending and receiving hosts.
Whether abbreviation is permitted depends on how your site is configured.
Domain names (i.e., anything after the ``@'' sign) may be given in any mixture
of upper and lower case. Most hosts accept any combination of case in user
names, although there are exceptions.
Every site is required to have a user or user alias designated ``postmaster'' to
which problems with the mail system may be addressed, for example:
postmaster@CS.Berkeley.EDU
Certain old address formats, such as UUCP ``bang path'' addresses, explicitly
routed internet addresses (so-called ``route-addrs'' and the ``percent hack'')
and others have been used historically. All these addressing formats are now
considered obsolete, and should no longer be used.
To some extent, MTAs attempt to provide backward compatibility for
these addressing forms, but in practice many of them no longer work. Users
should always use standard Internet style addresses.
mail(1)
D. H. Crocker,
Standard for the Format of Arpa Internet Text
Messages, RFC, 822,
August 1982.
mailaddr
appeared in 4.2BSD.
The RFC 822 group syntax (``group:user1,user2,user3;'') is not supported except
in the special case of ``group:;'' because of a conflict with old
berknet-style addresses, not that anyone cares about either berknet or group
syntax style addresses any longer.