MAILADDR(7)

NAME
mailaddr - mail addressing description

DESCRIPTION
Mail addresses are based on the ARPANET 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, the address

orc@brazil.pell.UUCP

is normally interpreted from right to left: the message should go to the pell.UUCP gateway, after which it should go to the local host brazil. When the message reaches brazil it is delivered to the user ‘orc’.

Unlike some other forms of addressing, this does not imply any routing. Thus, although this address is specified as an ARPA address, it might travel by an alternate route if that were more convenient or efficient. For example, at Pell, the associated message would probably go directly to brazil over the Ethernet rather than going via UUCP.

  Abbreviation.
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 ‘gehenna.pell.UUCP’ could send to ‘orc@brazil’ without adding the ‘pell.UUCP’ since it is the same on both sending and receiving hosts.

  Compatibility.
Certain old address formats are converted to the new format to provide compatibility with the previous mail system. In particular,

host:user
is converted to

user@host
to be consistent with the rcp(1) command.

Also, the syntax

host1!host2!...!hostN!user

is converted to:

host2!...!hostN!user@host1

When being sent through a TCP network. (Under the hope that the mail server at host1 will understand UUCP syntax too.)

  Case Distinctions.
Domain names (i.e., anything after the ``@'' sign) may be given in any mixture of upper and lower case with the exception of UUCP hostnames. Many hosts do NOT accept any combination of case in user names (MULTICS and many Unix hosts), so as a general rule you should assume that the user Orc is not the same person as orc.

  Postmaster.
Every site is required to have a user or user alias designated ‘postmaster’ to which problems with the mail system may be addressed.

BUGS
The RFC822 group syntax (``group:user1,user2,user3;'') is not supported.

UUCP- and ARPANET-style addresses do not coexist politely.

SEE ALSO
mail(1), postoffice(8);

DARPA Internet Request For Comments