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2 .\" The Regents of the University of California. All rights reserved.
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5 .\" modification, are permitted provided that the following conditions
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32 .\" @(#)mailaddr.7 8.1 (Berkeley) 6/16/93
40 .Nd mail addressing description
42 Mail addresses are based on the Internet protocol listed at the end of this
44 These addresses are in the general format
48 where a domain is a hierarchical dot separated list of subdomains.
50 example, a valid address is:
52 .Dl eric@CS.Berkeley.EDU
54 Unlike some other forms of addressing, domains do not imply any routing.
55 Thus, although this address is specified as an Internet address, it might
56 travel by an alternate route if that were more convenient or efficient.
57 For example, at Berkeley, the associated message would probably go directly
58 to CS over the Ethernet rather than going via the Berkeley Internet
61 Under certain circumstances it may not be necessary to type the entire
63 In general, anything following the first dot may be omitted
64 if it is the same as the domain from which you are sending the message.
65 For example, a user on ``calder.berkeley.edu'' could send to ``eric@CS''
66 without adding the ``berkeley.edu'' since it is the same on both sending
70 Certain old address formats are converted to the new format to provide
71 compatibility with the previous mail system.
95 This is normally converted back to the ``host!user'' form before being sent
96 on for compatibility with older UUCP hosts.
98 .Ss Case Distinctions.
100 Domain names (i.e., anything after the ``@'' sign) may be given in any mixture
101 of upper and lower case with the exception of UUCP hostnames.
103 accept any combination of case in user names, with the notable exception of
107 Under some circumstances it may be necessary to route a message through
108 several hosts to get it to the final destination.
109 Normally this routing
110 is done automatically, but sometimes it is desirable to route the message
112 Addresses which show these relays are termed ``route-addrs.''
113 These use the syntax:
115 .Dl <@hosta,@hostb:user@hostc>
117 This specifies that the message should be sent to hosta, from there to hostb,
118 and finally to hostc.
119 This path is forced even if there is a more efficient
122 Route-addrs occur frequently on return addresses, since these are generally
123 augmented by the software at each host.
124 It is generally possible to ignore
125 all but the ``user@hostc'' part of the address to determine the actual
128 [Note: the route-addr syntax is officially deprecated
129 in RFC 1123 and should not be used.]
131 Many sites also support the ``percent hack'' for simplistic routing:
133 .Dl user%hostc%hostb@hosta
135 is routed as indicated in the previous example.
138 Every site is required to have a user or user alias designated ``postmaster''
139 to which problems with the mail system may be addressed.
142 Some other networks can be reached by giving the name of the network as the
143 last component of the domain.
144 .Em This is not a standard feature
146 not be supported at all sites.
147 For example, messages to CSNET or BITNET sites
148 can often be sent to ``user@host.CSNET'' or ``user@host.BITNET'' respectively.
154 .%T Standard for the Format of Arpa Internet Text Messages
162 The RFC822 group syntax (``group:user1,user2,user3;'') is not supported
163 except in the special case of ``group:;'' because of a conflict with old
164 berknet-style addresses.
166 Route-Address syntax is grotty.
168 UUCP- and Internet-style addresses do not coexist politely.