MAILADDR(7)	    UNIX Programmer's Manual	      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 sub-
     domains.  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 gate-
     way, 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 Berke-
     ley, 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,





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MAILADDR(7)	    UNIX Programmer's Manual	      MAILADDR(7)



	       user@host.ARPA

     is allowed and

	       host:user

     is converted to

	       user@host

     to be consistent with the _r_c_p(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 excep-
     tion 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 mes-
     sage through several hosts to get it to the final destina-
     tion.  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.




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MAILADDR(7)	    UNIX Programmer's Manual	      MAILADDR(7)



     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.

     Postmaster.

     Every site is required to have a user or user alias desig-
     nated ``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.  _T_h_i_s _i_s _n_o_t _a
     _s_t_a_n_d_a_r_d _f_e_a_t_u_r_e 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), sendmail(8); Crocker, D. H., _S_t_a_n_d_a_r_d _f_o_r _t_h_e _F_o_r_-
     _m_a_t _o_f _A_r_p_a _I_n_t_e_r_n_e_t _T_e_x_t _M_e_s_s_a_g_e_s, RFC822.























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