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 was 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 (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 mixture of case in user names, 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.
At the time of this writing the only ``top level'' domain defined by ARPA is the ``.ARPA'' domain itself. This is further restricted to having only one level of host specifier. That is, the only addresses that ARPA accepts at this time must be in the format ``user@host.ARPA'' (where ``host'' is one word). In particular, addresses such as:
eric@monet.Berkeley.ARPA
are not currently legal under the ARPA protocols. For this reason, these addresses are converted to a different format on output to the ARPANET, typically:
eric%monet@Berkeley.ARPA
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. An address that shows 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.
CSNET. Messages to CSNET sites can be sent to ``user.host@UDel-Relay''.
Host Names. Many of the old familiar host names are being phased out. In particular, single character names as used in Berknet are incompatible with the larger world of which Berkeley is now a member. For this reason the following names are being obsoleted. You should notify any correspondents of your new address as soon as possible.
OLD NEW j ingvax ucbingres p ucbcad r arpavax ucbarpa v csvax ucbernie n ucbkim y ucbcory
The old addresses will be rejected as unknown hosts sometime in the near future.
What's My Address? If you are on a local machine, say monet, your address is
yourname@monet.Berkeley.ARPA
However, since most of the world does not have the new software in place yet, you will have to give correspondents slightly different addresses. From the ARPANET, your address would be:
yourname%monet@Berkeley.ARPA
From UUCP, your address would be:
ucbvax!yourname%monet
Computer Center. The Berkeley Computer Center is in a subdomain of Berkeley. Messages to the computer center should be addressed to:
user%host.CC@Berkeley.ARPA
The alternate syntax:
user@host.CC
may be used if the message is sent from inside Berkeley.
For the time being Computer Center hosts are known within the Berkeley domain, i.e., the ``.CC'' is optional. However, it is likely that this situation will change with time as both the Computer Science department and the Computer Center grow.
Bitnet. Hosts on bitnet may be accessed using:
user@host.BITNET