envelopes.5 (4847B)
1 .TH envelopes 5 2 .SH "NAME" 3 envelopes \- sender/recipient lists attached to messages 4 .SH "INTRODUCTION" 5 Electronic mail messages are delivered in 6 .IR envelopes . 7 8 An envelope lists a 9 .I sender 10 and one or more 11 .IR recipients . 12 Usually these 13 envelope addresses are the same 14 as the addresses listed in the message header: 15 16 .EX 17 (envelope) from djb to root 18 .br 19 From: djb 20 .br 21 To: root 22 .EE 23 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: 31 32 .EX 33 (envelope) from djb to root 34 .br 35 From: djb Copy #1 of message 36 .br 37 To: root, god@brl.mil 38 .EE 39 40 .EX 41 (envelope) from djb to god@brl.mil 42 .br 43 From: djb Copy #2 of message 44 .br 45 To: root, god@brl.mil 46 .EE 47 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: 54 55 .EX 56 (envelope) from djb to god@brl.mil, angel@brl.mil 57 .br 58 From: djb 59 .br 60 To: god@brl.mil, angel@brl.mil, joe, frde 61 .EE 62 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: 66 67 .EX 68 (envelope) from <> to djb 69 .br 70 From: MAILER-DAEMON 71 .br 72 To: djb 73 .br 74 Subject: unknown user frde 75 .EE 76 77 The recipient of a message may make another copy 78 and forward it in a new envelope: 79 80 .EX 81 (envelope) from djb to joe 82 .br 83 From: djb Original message 84 .br 85 To: joe 86 .EE 87 88 .EX 89 (envelope) from joe to fred 90 .br 91 From: djb Forwarded message 92 .br 93 To: joe 94 .EE 95 96 A mailing list works almost the same way: 97 98 .EX 99 (envelope) from djb to sos-list 100 .br 101 From: djb Original message 102 .br 103 To: sos-list 104 .EE 105 106 .EX 107 (envelope) from sos-owner to god@brl.mil 108 .br 109 From: djb Forwarded message 110 .br 111 To: sos-list to recipient #1 112 .EE 113 114 .EX 115 (envelope) from sos-owner to frde 116 .br 117 From: djb Forwarded message 118 .br 119 To: sos-list to recipient #2 120 .EE 121 122 Notice that the mailing list is set up 123 to replace the envelope sender with something new, 124 .BR sos-owner . 125 So bounces will come back to 126 .BR sos-owner : 127 128 .EX 129 (envelope) from <> to sos-owner 130 .br 131 From: MAILER-DAEMON 132 .br 133 To: sos-owner 134 .br 135 Subject: unknown user frde 136 .EE 137 138 It's a good idea to set up an extra address, 139 .BR sos-owner , 140 like this: 141 the original envelope sender (\fBdjb\fP) 142 has no way to fix bad 143 .B sos-list 144 addresses, 145 and of course bounces must not be sent to 146 .B sos-list 147 itself. 148 .SH "HOW ENVELOPE ADDRESSES ARE STORED" 149 Envelope sender and envelope recipient addresses 150 are transmitted and recorded in several ways. 151 152 When a user injects mail through 153 .BR qmail-inject , 154 he can supply a 155 .B Return-Path 156 line or a 157 .B \-f 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 163 .BR qmail-inject . 164 Similar comments apply to 165 .BR sendmail . 166 167 When a message is transferred from one machine to another through SMTP, 168 the envelope sender is given in a 169 .B MAIL FROM 170 command, 171 the envelope recipients are given in 172 .B RCPT TO 173 commands, 174 and the message is supplied separately by a 175 .B DATA 176 command. 177 178 When a message is delivered by 179 .B qmail 180 to a single local recipient, 181 .B qmail-local 182 records the recipient in 183 .B Delivered-To 184 and the envelope sender in 185 .BR Return-Path . 186 It uses 187 .B Delivered-To 188 to detect mail forwarding loops. 189 190 .B sendmail 191 normally records the envelope sender in 192 .BR Return-Path . 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. 197 198 Note that, 199 if the header doesn't have any recipient addresses, 200 .B sendmail 201 will move envelope recipient addresses back into the header. 202 This situation occurs if all addresses were originally listed as 203 .BR Bcc , 204 since 205 .B Bcc 206 is automatically removed. 207 When 208 .B sendmail 209 sees this, it creates a new 210 .B Apparently-To 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. 214 215 When a message is stored in 216 .B mbox 217 format, 218 the envelope sender is recorded at the top of the message 219 as a UUCP-style 220 .B From 221 (no colon) line. 222 Note that this line is less reliable than the 223 .B Return-Path 224 line added by 225 .B qmail-local 226 or 227 .B sendmail\fP. 228 .SH "SEE ALSO" 229 qmail-header(5), 230 qmail-local(8), 231 qmail-inject(8)