mailaddr(7)						 Miscellaneous Information Manual					       mailaddr(7)

Name
       mailaddr - mail addressing description

Description
       Mail  addresses	are  based on the ARPANET protocol listed in the SEE ALSO section of this reference page.  In addition, the DECnet address
       format can be used, if DECnet is installed on your system.

       To send mail to DECnet users, use the following address format:
       nodename::username
       In this case, nodename is the name of the DECnet system, or host, on which the target user resides.

       Addresses based on the ARPANET protocol use the following general format:
       user@domain
       A domain is a hierarchical dot-separated list of subdomains.  For example, the following address is interpreted from right to left:
       eric@monet.Berkeley.ARPA
       In the previous example, the message is directed to the ARPA name tables (which do not correspond exactly to the  physical  ARPANET).   The
       message then proceeds to the Berkeley gateway, after which it is directed to the local host When the message reaches it is delivered to the
       user

       Unlike some other forms of addressing, this does not imply any routing.	Thus, an address that is specified as an ARPA address  can  travel
       by an alternate route if that route is more convenient or efficient.  For example, from Berkeley, the message could go directly to over the
       Ethernet, rather than using the Berkeley ARPANET gateway.

       Abbreviations.  In some instances, you do not have to type an entire domain name.  Generally, any information that follows  the	first  dot
       may  be	omitted  if the sending and receiving domains are the same.  For example, a user on calder.Berkeley.ARPA can eliminate the .Berke-
       ley.ARPA when sending to eric@monet, because the sending and receiving hosts are the same.

       Other abbreviations are permitted when conflicts do not exist.  For example, Berkeley ARPANET hosts can	be  accessed  without  adding  the
       .ARPA, if their names do not conflict with a local host name.

       Compatible  Addresses.	To  provide compatibility with the previous mail system, some old address formats are converted to the new format.
       In particular, host::user is converted to user@host providing consistency with the command.

       The syntax host!user is converted to user@host.UUCP.  Before being sent on, user@host.UUCP is normally  converted  back	to  the  host!user
       form. This conversion is done for compatibility with older UUCP hosts.

       The  current  implementation  cannot automatically route messages through the UUCP network.  Thus, you must explicitly tell the mail system
       all the hosts your messages must be sent through to arrive at its final destination.

       Case Distinctions.  Domain names (that is, anything following the at sign (@)) can be a combination of upper- and lowercase characters with
       the exception of UUCP hostnames.  Most hosts accept both upper- and lowercase in user names, with the exception of MULTICS sites.

       Differences  with  ARPA Protocols.  Although the UNIX addressing scheme is based on the ARPA mail addressing protocols, there are some sig-
       nificant differences.

       Currently, the only top level domain defined by ARPA is the .ARPA domain itself.  This is further restricted to having only  one  level	of
       host  specifier.   That	is, the addresses that ARPA accepts must be in the format user@host.ARPA (where `host' is one word).  For example,
       the following address is not legal under the ARPA protocols:
       eric@monet.Berkeley.ARPA
       Thus, the previous address would be converted to a different format on output to the ARPANET.  For example:
       eric%monet@Berkeley.ARPA
       Route-addrs.  In some instances, a message must be routed through several hosts to reach its final destination.	Usually,  this	action	is
       invisible  to  the  sender;  however,  it is sometimes desirable to route a message manually.  Addresses that are moved manually are called
       route-addrs.  The syntax is as follows:
       <@hosta,@hostb:user@hostc>
       The previous example directs the message to hosta, to hostb, and finally to hostc.  This route is used regardless of a more efficient  path
       to hostc.

       Route-addrs  occur  frequently  on  return addresses, because they are generally augmented by the software at each host.  It is possible to
       ignore all but the user@host part of the address to determine the actual sender.

       Postmaster.  Every site must have a user or user alias designated as postmaster to which problems with the mail system can be addressed.

       CSNET.  To send messages to CSNET, use the following syntax:
       user.host@UDel-Relay

See Also
       mail(1), sendmail(8)
       Crocker, D. H., Standard for the Format of Arpa Internet Text Messages, RFC822

																       mailaddr(7)