MAILADDR(7)MAILADDR(7)NAMEmailaddr - mail addressing description
Mail addresses are based on the ARPANET 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, the address
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
Under certain circumstances it may not be necessary to type the entire
domain name. In general, anything following the first dot may be omit‐
ted if it is the same as the domain from which you are sending the mes‐
sage. For example, 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.
Certain old address formats are converted to the new format to provide
compatibility with the previous mail system. In particular,
is allowed and
is converted to
to be consistent with the rcp(1) command.
Also, the syntax
is converted to:
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
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 rout‐
ing 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 gen‐
erally augmented by the software at each host. It is generally possi‐
ble to ignore all but the ``user@domain'' part of the address to deter‐
mine the actual sender.
Every site is required to have a user or user alias designated ``post‐
master'' to which problems with the mail system may be addressed.
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
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 ALSOmail(1), sendmail(8); Crocker, D. H., Standard for the Format of Arpa
Internet Text Messages, RFC822.
4.2 Berkeley Distribution February 14, 1989 MAILADDR(7)