.\" Copyright (c) 1983, 1987 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms are permitted
.\" provided that the above copyright notice and this paragraph are
.\" duplicated in all such forms and that any documentation,
.\" advertising materials, and other materials related to such
.\" distribution and use acknowledge that the software was developed
.\" by the University of California, Berkeley.  The name of the
.\" University may not be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
.\"	@(#)mailaddr.7	6.5 (Berkeley) 2/14/89
.\"
.Dd February 14, 1989
.Dt MAILADDR 7 
.Os BSD 4
.Sh NAME
.Nm mailaddr 
.Nd mail addressing description
.Sh DESCRIPTION
Mail addresses are based on the ARPANET protocol listed at the end of this
manual page.  These addresses are in the general format
.Pp
.Bd -ragged -offset indent-two
.Li user@domain
.Ed
.Pp
where a domain is a hierarchical, dot-separated list of subdomains.  For
example, the address
.Pp
.Bd -ragged -offset indent-two
.Li eric@monet.berkeley.edu
.Ed
.Pp
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
.Dq Li monet .  
When the message reaches 
.Li monet , 
it is delivered to the user 
.Dq Li eric .
.Pp
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 
.Li monet 
over the Ethernet rather than going via the Berkeley ARPANET gateway.
.Ss Abbreviation
.Pp
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 
.Dq Li calder.berkeley.edu 
could send to 
.Dq Li eric@monet
without adding the 
.Dq Li berkeley.edu 
since it is the same on both sending and receiving hosts.
.Pp
Certain other abbreviations may be permitted as special cases.  For
example, at Berkeley, ARPANET hosts may be referenced without adding the 
.Dq Li berkeley.edu 
as long as their names do not conflict with a local host name.
.Ss Compatibility
.Pp
Certain old address formats are converted to the new format to provide
compatibility with the previous mail system.  In particular,
.Bd -ragged -offset indent-two
.Li user@host.ARPA
.Ed
.Pp
is allowed and
.Bd -ragged -offset indent-two
.Li host:user
.Ed
.Pp
is converted to
.Bd -ragged -offset indent-two
.Li user@host
.Ed
.Pp
in order to be consistent with the 
.Xr rcp 1 
command.
.Pp
Also, the syntax
.Bd -ragged -offset indent-two
.Li host!user
.Ed
.Pp
is converted to:
.Bd -ragged -offset indent-two
.Li user@host.UUCP
.Ed
.Pp
This is normally converted back to the 
.Dq Li host!user 
form before being sent on, for compatibility with older UUCP hosts.
.Pp
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.
.Ss Case Distinctions
.Pp
Domain names (i.e., anything after the 
.Dq Li @ 
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.
.Ss Route-addrs.
.Pp
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 
.Dq route-addrs.
These use the syntax:
.Bd -ragged -offset indent-two
.Li <@hosta,@hostb:user@hostc>
.Ed
.Pp
This specifies that the message should be sent to 
.Li hosta , 
from there to 
.Li hostb ,
and finally to 
.Li hostc .  
This path is forced even if there is a more efficient path to 
.Li hostc .
.Pp
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 
.Dq Li user@domain 
part of the address to determine the actual sender.
.Ss Postmaster
.Pp
Every site is required to have a user or user alias designated 
.Dq Li postmaster
to which problems with the mail system may be addressed.
.Ss Other Networks
.Pp
Some other networks can be reached by giving the name of the network as the
last component of the domain.  
.Em This is not a standard feature
and may
.Em not 
be supported at all sites.  For example, messages to CSNET or BITNET sites
can often be sent to 
.Dq Li user@host.CSNET 
or 
.Dq Li user@host.BITNET , 
respectively.
.Sh BUGS
The RFC822 group syntax 
.Pq Dq Li group:user1,user2,user3; 
is not supported except in the special case of 
.Dq LI group:; 
because of a conflict with old berknet-style addresses.
.Pp
Route-Address syntax is grotty.
.Pp
UUCP- and ARPANET-style addresses do not coexist politely.
.Sh SEE ALSO
.Xr mail 1 , 
.Xr sendmail 8 ;
Crocker, D. H., RFC822, 
.Do
Standard for the Format of Arpa Internet Text Messages
.Dc .