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MAILADDR(7)          BSD Miscellaneous Information Manual          MAILADDR(7)

     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


     where a domain is a hierarchical dot separated list of subdomains.  For
     example, a valid address is:


     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 ``userATsomedomain.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 sendmail(8), 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.

   Case Distinctions
     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 ``postmas-
     ter'' to which problems with the mail system may be addressed, for exam-


   Obsolete Formats
     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

     To some extent, sendmail(8) (when running with normal configuration
     files) attempts 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), sendmail(8)

     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.

BSD                              June 16, 1998                             BSD