3 envelopes \- sender/recipient lists attached to messages
5 Electronic mail messages are delivered in
13 envelope addresses are the same
14 as the addresses listed in the message header:
17 (envelope) from djb to root
24 In more complicated situations, though,
25 the envelope addresses may differ from the header addresses.
26 .SH "ENVELOPE EXAMPLES"
27 When a message is delivered to
28 several people at different locations,
29 it is first photocopied
30 and placed into several envelopes:
33 (envelope) from djb to root
35 From: djb Copy #1 of message
41 (envelope) from djb to god@brl.mil
43 From: djb Copy #2 of message
48 When a message is delivered
49 to several people at the same location,
50 the sender doesn't have to photocopy it.
51 He can instead stuff it into
52 one envelope with several addresses;
53 the recipients will make the photocopy:
56 (envelope) from djb to god@brl.mil, angel@brl.mil
60 To: god@brl.mil, angel@brl.mil, joe, frde
63 Bounced mail is sent back to the envelope sender address.
64 The bounced mail doesn't list an envelope sender,
65 so bounce loops are impossible:
68 (envelope) from <> to djb
74 Subject: unknown user frde
77 The recipient of a message may make another copy
78 and forward it in a new envelope:
81 (envelope) from djb to joe
83 From: djb Original message
89 (envelope) from joe to fred
91 From: djb Forwarded message
96 A mailing list works almost the same way:
99 (envelope) from djb to sos-list
101 From: djb Original message
107 (envelope) from sos-owner to god@brl.mil
109 From: djb Forwarded message
111 To: sos-list to recipient #1
115 (envelope) from sos-owner to frde
117 From: djb Forwarded message
119 To: sos-list to recipient #2
122 Notice that the mailing list is set up
123 to replace the envelope sender with something new,
125 So bounces will come back to
129 (envelope) from <> to sos-owner
135 Subject: unknown user frde
138 It's a good idea to set up an extra address,
141 the original envelope sender (\fBdjb\fP)
142 has no way to fix bad
145 and of course bounces must not be sent to
148 .SH "HOW ENVELOPE ADDRESSES ARE STORED"
149 Envelope sender and envelope recipient addresses
150 are transmitted and recorded in several ways.
152 When a user injects mail through
158 option for the envelope sender;
159 by default the envelope sender is his login name.
160 The envelope recipient addresses can be taken
161 from the command line or from various header fields,
162 depending on the options to
164 Similar comments apply to
167 When a message is transferred from one machine to another through SMTP,
168 the envelope sender is given in a
171 the envelope recipients are given in
174 and the message is supplied separately by a
178 When a message is delivered by
180 to a single local recipient,
182 records the recipient in
184 and the envelope sender in
188 to detect mail forwarding loops.
191 normally records the envelope sender in
193 It does not record envelope recipient addresses,
194 on the theory that they are redundant:
195 you received the mail,
196 so you must have been one of the envelope recipients.
199 if the header doesn't have any recipient addresses,
201 will move envelope recipient addresses back into the header.
202 This situation occurs if all addresses were originally listed as
206 is automatically removed.
209 sees this, it creates a new
211 header field with the envelope recipient addresses.
212 This has the strange effect that each blind-carbon-copy recipient will see
213 a list of all recipients on the same machine.
215 When a message is stored in
218 the envelope sender is recorded at the top of the message
222 Note that this line is less reliable than the
~mdw / qmail / blob