Manual Reference Pages - MAILADDR (7)
- mail addressing description
Mail addresses are based on the Internet protocol listed at the end of this
These addresses are in the general format
where a domain is a hierarchical dot separated list of subdomains.
example, a valid address is:
Unlike some other forms of addressing, domains do not imply any routing.
Thus, although this address is specified as an Internet 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 CS over the Ethernet rather than going via the Berkeley Internet
Under certain circumstances it may not be necessary to type the entire
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.
Certain old address formats are converted to the new format to provide
compatibility with the previous mail system.
is converted to
is converted to
This is normally converted back to the host!user form before being sent
on for compatibility with older UUCP hosts.
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.
accept any combination of case in user names, with the notable exception of
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
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
[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.
Every site is required to have a user or user alias designated postmaster
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
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.
Standard for the Format of Arpa Internet Text Messages
BSD 4.2 .
The RFC822 group syntax (group:user1,user2,user3;) is not supported
except in the special case of group:; because of a conflict with old
Route-Address syntax is grotty.
UUCP- and Internet-style addresses do not coexist politely.
Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.