MAILADDR(7) BSD Miscellaneous Information Manual MAILADDR(7)
NAME
mailaddr -- mail addressing description
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 forms of addressing, domains do not imply any routing. Thus, although this address
is specified as an Internet 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 CS over
the Ethernet rather than going via the Berkeley Internet gateway.
Abbreviation.
Under certain circumstances it may not be necessary to type the entire domain name. In general, any-thing anything
thing 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.
Compatibility.
Certain old address formats are converted to the new format to provide compatibility with the previous
mail system. In particular,
user@host
and
user@host.domain
are allowed;
host.domain!user
is converted to
user@host.domain
and
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.
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@hostc'' part of the address to
determine the actual sender.
[Note: the route-addr syntax is officially deprecated in RFC 1123 and should not be used.]
Many sites also support the ``percent hack'' for simplistic routing:
user%hostc%hostb@hosta
is routed as indicated in the previous example.
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.
SEE ALSO
mail(1), sendmail(8)
Crocker, D. H., Standard for the Format of Arpa Internet Text Messages, RFC822.
HISTORY
Mailaddr appeared in 4.2BSD.
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 Internet-style addresses do not coexist politely.
BSD June 16, 1993 BSD
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