mailaddr - mail addressing description
Mail addresses are based on the ARPANET protocol listed atthe end of this manual page. These addresses are in thegeneral format
user@domain
where a domain is a hierarchical dot separated list ofsubdomains. For example, the address
eric@monet.berkeley.edu
is normally interpreted from right to left: the messageshould go to the ARPA name tables (which do not correspondexactly to the physical ARPANET), then to the Berkeleygateway, 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 implyany routing. Thus, although this address is specified asan ARPA address, it might travel by an alternate route ifthat were more convenient or efficient. For example, atBerkeley, the associated message would probably godirectly to monet over the Ethernet rather than going viathe Berkeley ARPANET gateway.
Abbreviation.
Under certain circumstances it may not be necessary totype the entire domain name. In general, anything followingthe first dot may be omitted if it is the same as thedomain from which you are sending the message. For example,a user on ``calder.berkeley.edu'' could send to``eric@monet'' without adding the ``berkeley.edu'' sinceit is the same on both sending and receiving hosts.
Certain other abbreviations may be permitted as specialcases. For example, at Berkeley, ARPANET hosts may bereferenced without adding the ``berkeley.edu'' as long astheir names do not conflict with a local host name.
Compatibility.
Certain old address formats are converted to the new formatto provide compatibility with the previous mail system.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'' formbefore being sent on for compatibility with older UUCPhosts.
The current implementation is not able to route messagesautomatically through the UUCP network. Until that timeyou must explicitly tell the mail system which hosts tosend your message through to get to your final destination.
Case Distinctions.
Domain names (i.e., anything after the ``@'' sign) may begiven in any mixture of upper and lower case with theexception of UUCP hostnames. Most hosts accept any combinationof case in user names, with the notable exceptionof MULTICS sites.
Route-addrs.
Under some circumstances it may be necessary to route amessage 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 isforced even if there is a more efficient path to hostc.
Route-addrs occur frequently on return addresses, sincethese are generally augmented by the software at eachhost. It is generally possible to ignore all but the``user@domain'' part of the address to determine theactual sender.
Postmaster.
Every site is required to have a user or user alias designated``postmaster'' to which problems with the mailsystem may be addressed.
Other Networks.
Some other networks can be reached by giving the name ofthe network as the last component of the domain. This isnot a standard feature and may not be supported at allsites. For example, messages to CSNET or BITNET sites canoften be sent to ``user@host.CSNET'' or``user@host.BITNET'' respectively.
The RFC822 group syntax (``group:user1,user2,user3;'') isnot 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.
mail(1), sendmail(8); Crocker, D. H., Standard for theFormat of Arpa Internet Text Messages, RFC822.