MAILADDR(7) UNIX 5.0 (July 27, 1987) 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
eric@monet.berkeley.edu
is normally interpreted from right to left: the message
should go to the ARPA name tables (which do not correspond
exactly to the physical ARPANET), then to the Berkeley
gateway, after which it should go to the local host monet.
When the message reaches monet it is delivered to the user
``eric''.
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
Berkeley, the associated message would probably go directly
to monet over the Ethernet rather than going via the
Berkeley ARPANET gateway.
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 ``calder.berkeley.edu'' could send to ``eric@monet''
without adding the ``berkeley.edu'' since it is the same on
both sending and receiving hosts.
Certain other abbreviations may be permitted as special
cases. For example, at Berkeley, ARPANET hosts may be
referenced without adding the ``berkeley.edu'' as long as
their names do not conflict with a local host name.
Compatibility.
Certain old address formats are converted to the new format
to provide compatibility with the previous mail system. In
particular,
user@host.ARPA
is allowed and
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MAILADDR(7) UNIX 5.0 (July 27, 1987) MAILADDR(7)
host:user
is converted to
user@host
to be consistent with the rcp(1) command.
Also, the syntax
host!user
is converted to:
user@host.UUCP
This is normally converted back to the ``host!user'' form
before being sent on for compatibility with older UUCP
hosts.
The current implementation is not able to route messages
automatically through the UUCP network. Until that time you
must explicitly tell the mail system which hosts to send
your message through to get to your final destination.
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. Most hosts accept any
combination of case in user names, with the notable
exception of MULTICS sites.
Route-addrs.
Under some circumstances it may be necessary to route a
message through several hosts to get it to the final
destination. Normally this routing is done automatically,
but sometimes it is desirable to route the message manually.
Addresses which show these relays are termed ``route-
addrs.'' These use the syntax:
<@hosta,@hostb:user@hostc>
This specifies that the message should be sent to hosta,
from there to hostb, and finally to hostc. This path is
forced even if there is a more efficient path 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@domain'' part of the address to determine the actual
sender.
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Postmaster.
Every site is required to have a user or user alias
designated ``postmaster'' to which problems with the mail
system may be addressed.
Other Networks.
Some other networks can be reached by giving the name of the
network as the last component of the domain. This is not a
standard feature and may not be supported at all sites. For
example, messages to CSNET or BITNET sites can often be sent
to ``user@host.CSNET'' or ``user@host.BITNET'' respectively.
BUGS
The RFC822 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.
Route-Address syntax is grotty.
UUCP- and ARPANET-style addresses do not coexist politely.
SEE ALSO
mail(1) ; Crocker, D. H., Standard for the
Format of Arpa Internet Text Messages, RFC822.
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