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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 forms of	addressing, domains do not imply any routing.
     Thus, although this address is specified as an Internet 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	di-
     rectly to CS over the Ethernet rather than	going via the Berkeley Inter-
     net gateway.

     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 ``'' could send to ``eric@CS''
     without adding the	``'' since it is the same on both sending
     and receiving hosts.

     Certain old address formats are converted to the new format to provide
     compatibility with	the previous mail system.  In particular,



     are allowed;


     is	converted to




     is	converted to


     This is normally converted	back to	the ``host!user'' form before being
     sent on for compatibility with older UUCP hosts.

   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 combination of case in user names, with the notable
     exception of MULTICS sites.

     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:


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

     [Note: the	route-addr syntax is officially	deprecated in RFC 1123 and
     should not	be used.]

     Many sites	also support the ``percent hack'' for simplistic routing:


     is	routed as indicated in the previous example.

     Every site	is required to have a user or user alias designated ``postmas-
     ter'' 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''

     mail(1), sendmail(8)

     Crocker, D. H., Standard for the Format of	Arpa Internet Text Messages,

     Mailaddr appeared in 4.2BSD.

     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 Internet-style addresses	do not coexist politely.

BSD				 June 16, 1993				   BSD


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