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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.edu” could send to “eric@CS” without adding the “berkeley.edu” since it is the same on both sending and receiving hosts.

Compatibility

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

and

are allowed;

is converted to

and

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.

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. 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 generally 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.

Postmaster

Every site is required to have a user or user alias designated “postmaster” 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”, respectively.