Uniformly refer to RFCs as 'RFC xxxx' and not 'RFCxxxx' or 'RFC-xxxx'.
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1.\" Copyright (c) 1983, 1987, 1990, 1993
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32.\" @(#)mailaddr.7 8.1 (Berkeley) 6/16/93
33.\" $FreeBSD: src/share/man/man7/mailaddr.7,v 1.6.2.1 2001/08/17 13:08:49 ru Exp $
cabeba47 34.\" $DragonFly: src/share/man/man7/mailaddr.7,v 1.5 2007/11/23 23:16:37 swildner Exp $
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35.\"
36.Dd June 16, 1993
37.Dt MAILADDR 7
38.Os
39.Sh NAME
40.Nm mailaddr
41.Nd mail addressing description
42.Sh DESCRIPTION
43Mail addresses are based on the Internet protocol listed at the end of this
44manual page. These addresses are in the general format
45.Pp
46.Dl user@domain
47.Pp
48where a domain is a hierarchical dot separated list of subdomains. For
49example, a valid address is:
50.Pp
51.Dl eric@CS.Berkeley.EDU
52.Pp
53Unlike some other forms of addressing, domains do not imply any routing.
54Thus, although this address is specified as an Internet address, it might
55travel by an alternate route if that were more convenient or efficient.
56For example, at Berkeley, the associated message would probably go directly
57to CS over the Ethernet rather than going via the Berkeley Internet
58gateway.
59.Ss Abbreviation.
60Under certain circumstances it may not be necessary to type the entire
61domain name. In general, anything following the first dot may be omitted
62if it is the same as the domain from which you are sending the message.
63For example, a user on ``calder.berkeley.edu'' could send to ``eric@CS''
64without adding the ``berkeley.edu'' since it is the same on both sending
65and receiving hosts.
66.Ss Compatibility.
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67Certain old address formats are converted to the new format to provide
68compatibility with the previous mail system. In particular,
69.Pp
70.Dl user@host
71.Pp
72and
73.Dl user@host.domain
74.Pp
75are allowed;
76.Pp
77.Dl host.domain!user
78.Pp
79is converted to
80.Pp
81.Dl user@host.domain
82.Pp
83and
84.Pp
85.Dl host!user
86.Pp
87is converted to
88.Pp
89.Dl user@host.UUCP
90.Pp
91This is normally converted back to the ``host!user'' form before being sent
92on for compatibility with older UUCP hosts.
984263bc 93.Ss Case Distinctions.
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94Domain names (i.e., anything after the ``@'' sign) may be given in any mixture
95of upper and lower case with the exception of UUCP hostnames. Most hosts
96accept any combination of case in user names, with the notable exception of
97MULTICS sites.
98.Ss Route-addrs.
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99Under some circumstances it may be necessary to route a message through
100several hosts to get it to the final destination. Normally this routing
101is done automatically, but sometimes it is desirable to route the message
102manually. Addresses which show these relays are termed ``route-addrs.''
103These use the syntax:
104.Pp
105.Dl <@hosta,@hostb:user@hostc>
106.Pp
107This specifies that the message should be sent to hosta, from there to hostb,
108and finally to hostc. This path is forced even if there is a more efficient
109path to hostc.
110.Pp
111Route-addrs occur frequently on return addresses, since these are generally
112augmented by the software at each host. It is generally possible to ignore
113all but the ``user@hostc'' part of the address to determine the actual
114sender.
115.Pp
116[Note: the route-addr syntax is officially deprecated
117in RFC 1123 and should not be used.]
118.Pp
119Many sites also support the ``percent hack'' for simplistic routing:
120.Pp
121.Dl user%hostc%hostb@hosta
122.Pp
123is routed as indicated in the previous example.
124.Ss Postmaster.
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125Every site is required to have a user or user alias designated ``postmaster''
126to which problems with the mail system may be addressed.
127.Ss Other Networks.
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128Some other networks can be reached by giving the name of the network as the
129last component of the domain.
130.Em This is not a standard feature
131and may
132not be supported at all sites. For example, messages to CSNET or BITNET sites
133can often be sent to ``user@host.CSNET'' or ``user@host.BITNET'' respectively.
134.Sh SEE ALSO
135.Xr mail 1 ,
136.Xr sendmail 8
137.Rs
138.%A Crocker, D. H.
139.%T Standard for the Format of Arpa Internet Text Messages
cabeba47 140.%O RFC 822
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141.Re
142.Sh HISTORY
143.Nm Mailaddr
144appeared in
145.Bx 4.2 .
146.Sh BUGS
cabeba47 147The RFC 822 group syntax (``group:user1,user2,user3;'') is not supported
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148except in the special case of ``group:;'' because of a conflict with old
149berknet-style addresses.
150.Pp
151Route-Address syntax is grotty.
152.Pp
153UUCP- and Internet-style addresses do not coexist politely.