mdw@git.distorted.org.uk Git - qmail/blob - qmail-header.5

   1 .TH qmail-header 5
   2 .SH NAME
   3 qmail-header \- format of a mail message
   4 .SH OVERVIEW
   5 At the top of every mail message is a
   6 highly structured
   7 .BR header .
   8 Many programs expect the header to carry certain information,
   9 as described below.
  10 The main function of
  11 .B qmail-inject
  12 is to make sure that each outgoing message has an appropriate header.
  13
  14 For more detailed information, see
  15 .BR http://pobox.com/~djb/proto/immhf.html .
  16 .SH "MESSAGE STRUCTURE"
  17 A message contains a series of
  18 .I header fields\fR,
  19 a blank line,
  20 and a
  21 .IR body :
  22
  23 .EX
  24      Received: (qmail-queue invoked by uid 666);
  25 .br
  26              30 Jul 1996 11:54:54 -0000
  27 .br
  28      From: djb@silverton.berkeley.edu (D. J. Bernstein)
  29 .br
  30      To: fred@silverton.berkeley.edu
  31 .br
  32      Date: 30 Jul 1996 11:54:54 -0000
  33 .br
  34      Subject: Go, Bears!
  35 .br
  36
  37 .br
  38      I've got money on this one.  How about you?
  39 .br
  40
  41 .br
  42      ---Dan   (this is the third line of the body)
  43 .EE
  44
  45 Each header field has a
  46 .IR name ,
  47 a colon,
  48 some
  49 .IR contents ,
  50 and a newline:
  51
  52 .EX
  53      Subject: Go, Bears!
  54 .EE
  55
  56 The field contents may be folded across several lines.
  57 Each line past the first must begin with a space or tab:
  58
  59 .EX
  60      Received: (qmail-queue invoked by uid 666);
  61 .br
  62              30 Jul 1996 11:54:54 -0000
  63 .EE
  64
  65 The field name must not contain spaces, tabs, or colons.
  66 Also, an empty field name is illegal.
  67 .B qmail-inject
  68 does not allow field names with unprintable characters.
  69
  70 Case is irrelevant in field names:
  71 .B subject
  72 and
  73 .B SUBJECT
  74 and
  75 .B SuBjEcT
  76 have the same meaning.
  77 .SH "ADDRESS LISTS"
  78 Certain fields, such as
  79 .BR To ,
  80 contain
  81 .I address lists\fR.
  82
  83 An address list contains some number of
  84 .I addresses
  85 or
  86 .I address groups\fR,
  87 separated by commas:
  88
  89 .EX
  90      a@b, c@d (Somebody), A Person <e@f>,
  91 .br
  92         random group: g@h, i@j;, k@l
  93 .EE
  94
  95 An
  96 .I address group
  97 has some text, a colon, a list of addresses,
  98 and a semicolon:
  99
 100 .EX
 101         random group: g@h, i@j;
 102 .EE
 103
 104 An address can appear in several forms.
 105 The most common form is
 106 .IR box@host .
 107
 108 Every address must include a host name.
 109 If
 110 .B qmail-inject
 111 sees a lone box name
 112 it adds the
 113 .I default host name\fR.
 114
 115 All host names should be fully qualified.
 116 .B qmail-inject
 117 appends the
 118 .I default domain name
 119 to any name without dots:
 120
 121 .EX
 122      djb@silverton  ->  djb@silverton.berkeley.edu
 123 .EE
 124
 125 It appends the
 126 .I plus domain name
 127 to any name
 128 that ends with a plus sign:
 129
 130 .EX
 131      eric@mammoth.cs+  ->  eric@mammoth.cs.berkeley.edu
 132 .EE
 133
 134 A host name may be a dotted-decimal address:
 135
 136 .EX
 137      djb@[128.32.183.163]
 138 .EE
 139
 140 RFC 822 allows mailbox names inside angle brackets
 141 to include
 142 .I source routes\fR,
 143 but
 144 .B qmail-inject
 145 strips all source routes out of addresses.
 146 .SH "SENDER ADDRESSES"
 147 .B qmail-inject
 148 looks for sender address lists in the following fields:
 149 .BR Sender ,
 150 .BR From ,
 151 .BR Reply-To ,
 152 .BR Return-Path ,
 153 .BR Return-Receipt-To ,
 154 .BR Errors-To ,
 155 .BR Resent-Sender ,
 156 .BR Resent-From ,
 157 .BR Resent-Reply-To .
 158
 159 If there is no
 160 .B From
 161 field,
 162 .B qmail-inject
 163 adds a new
 164 .B From
 165 field with the name of the user invoking
 166 .B qmail-inject.
 167
 168 RFC 822 requires that certain sender fields contain
 169 only a single address, but
 170 .B qmail-inject
 171 does not enforce this restriction.
 172 .SH "RECIPIENT ADDRESSES"
 173 .B qmail-inject
 174 looks for recipient address lists in the following fields:
 175 .BR To ,
 176 .BR Cc ,
 177 .BR Bcc ,
 178 .BR Apparently-To ,
 179 .BR Resent-To ,
 180 .BR Resent-Cc ,
 181 .BR Resent-Bcc .
 182
 183 Every message must contain at least one
 184 .B To
 185 or
 186 .B Cc
 187 or
 188 .BR Bcc .
 189 .B qmail-inject
 190 deletes any
 191 .B Bcc
 192 field.
 193 If there is no
 194 .B To
 195 or
 196 .B Cc
 197 field,
 198 .B qmail-inject
 199 adds a line
 200
 201 .EX
 202      Cc: recipient list not shown: ;
 203 .EE
 204
 205 This complies with RFC 822;
 206 it also works around some strange
 207 .B sendmail
 208 behavior, in case the message is passed through
 209 .B sendmail
 210 on another machine.
 211 .SH STAMPS
 212 Every message must contain a
 213 .B Date
 214 field, with the date in a strict format defined by RFC 822.
 215 If necessary
 216 .B qmail-inject
 217 creates a new
 218 .B Date
 219 field with the current date (in GMT).
 220
 221 Every message should contain a
 222 .B Message-Id
 223 field.
 224 The field contents are a unique worldwide identifier for this message.
 225 If necessary
 226 .B qmail-inject
 227 creates a new
 228 .B Message-Id
 229 field.
 230
 231 Another important field is
 232 .BR Received .
 233 Every time the message is sent from one system to another,
 234 a new
 235 .B Received
 236 field is added to the top of the message.
 237 .B qmail-inject
 238 does not create any
 239 .B Received
 240 fields.
 241 .SH "RESENT MESSAGES"
 242 A message is
 243 .I resent
 244 if it contains any of the following fields:
 245 .BR Resent-Sender ,
 246 .BR Resent-From ,
 247 .BR Resent-Reply-To ,
 248 .BR Resent-To ,
 249 .BR Resent-Cc ,
 250 .BR Resent-Bcc ,
 251 .BR Resent-Date ,
 252 .BR Resent-Message-ID .
 253
 254 If a message is resent,
 255 .B qmail-inject
 256 changes its behavior as follows.
 257
 258 It deletes any
 259 .B Resent-Bcc
 260 field (as well as any
 261 .B Bcc
 262 field);
 263 if there are no
 264 .B Resent-To
 265 or
 266 .B Resent-Cc
 267 fields,
 268 .B qmail-inject
 269 adds an appropriate
 270 .B Resent-Cc
 271 line.
 272 It does
 273 .I not
 274 add a
 275 .B Cc
 276 line,
 277 even if neither
 278 .B To
 279 nor
 280 .B Cc
 281 is present.
 282
 283 If there is no
 284 .B Resent-From
 285 field,
 286 .B qmail-inject
 287 adds a new
 288 .B Resent-From
 289 field.
 290 It does
 291 .I not
 292 add a new
 293 .B From
 294 field.
 295
 296 .B qmail-inject
 297 adds
 298 .B Resent-Date
 299 if one is not already present;
 300 same for
 301 .BR Resent-Message-Id .
 302 It does
 303 .I not
 304 add new
 305 .B Date
 306 or
 307 .B Message-Id
 308 fields.
 309 .SH "OTHER FEATURES"
 310 Addresses are separated by commas, not spaces.
 311 When
 312 .B qmail-inject
 313 sees an illegal space,
 314 it inserts a comma:
 315
 316 .EX
 317      djb fred  ->  djb, fred
 318 .EE
 319
 320 .B qmail-inject
 321 removes all
 322 .B Return-Path
 323 header fields.
 324
 325 .B qmail-inject
 326 also removes any
 327 .B Content-Length
 328 fields.
 329 .SH "SEE ALSO"
 330 addresses(5),
 331 envelopes(5),
 332 qmail-inject(8)