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, 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.

   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 gener-
     ally 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 ``postmas-
     ter'' 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