MAILADDR(7)                          BSD                           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 subdomains.  For
     example, the address

               eric@monet.Berkeley.ARPA

     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 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.ARPA could send to eric@monet
     without adding the .Berkeley.ARPA 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 can be referenced without adding the
     .ARPA 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,

               host:user

     is converted to

               user@host

     to be consistent with the rcp(1C) 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 (that is, anything after the "@" sign) may be given in any
     mixture of upper and lowercase with the exception of UUCP hostnames.
     Most hosts accept any combination of case in usernames, with the notable
     exception of MULTICS sites.

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

     DARPA has converted to real domains.  The following rules may be useful:

     ⊕  The syntax user@host.ARPA has been split up into user@host.COM,
        user@host.GOV, and user@host.EDU for commercial, government, and
        educational institutions, respectively.

     ⊕  The syntax user@host (with no dots) has traditionally referred to the
        ARPANET.  In the future, this semantic will not be continued -
        instead, the host will be assumed to be in your organization.  You
        should start using one of the syntaxes above.

     ⊕  Host names of the form ORG-NAME (for example, MIT-MC or CMU-CS-A) has
        been changed to NAME.ORG.XXX (where XXX is COM, GOV, or EDU).  For
        example, MIT-MC has been changed to MC.MIT.EDU.  In some cases, names
        were split apart even if they did not have dashes.  For example, USC-
        ISIF changed to F.ISI.USC.EDU.

   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
     generally augmented by the software at each host.  It is generally
     possible to ignore all but the user@host part of the address to determine
     the actual sender.

   Postmaster.
     Every site is required to have a user or user alias designated
     "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.

     UUCP- and ARPANET-style addresses do not coexist politely.

SEE ALSO
     mail(1), sendmail(8);
     Using Your BSD Environment;
     Crocker, D. H., Standard for the Format of Arpa Internet Text Messages,
     RFC822.