mailaddr

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
       subdomains.  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
       gateway, 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
       Berkeley,   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 follow-
       ing  the first dot may be omitted if it is the same as the
       domain from which you are sending the message.  For  exam-
       ple,  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  for-
       mat  to  provide compatibility with the previous mail sys-
       tem.  In particular,

                 user@host.ARPA

       is allowed and

                 host:user

       is converted to

                 user@host

       to be consistent with the rcp(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 destina-
       tion.

   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 combi-
       nation  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 des-
       tination.  Normally this routing  is  done  automatically,
       but  sometimes  it is desirable to route the message manu-
       ally.   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@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.  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.

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., Standard for the
       Format of Arpa Internet Text Messages, RFC822.