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 RFC 822 and RFC 1123.
  15 .SH "MESSAGE STRUCTURE"
  16 A message contains a series of
  17 .I header fields\fR,
  18 a blank line,
  19 and a
  20 .IR body :
  21
  22 .EX
  23      Received: (qmail-queue invoked by uid 666);
  24 .br
  25              30 Jul 1996 11:54:54 -0000
  26 .br
  27      From: djb@silverton.berkeley.edu (D. J. Bernstein)
  28 .br
  29      To: fred@silverton.berkeley.edu
  30 .br
  31      Date: 30 Jul 1996 11:54:54 -0000
  32 .br
  33      Subject: Go, Bears!
  34 .br
  35
  36 .br
  37      I've got money on this one.  How about you?
  38 .br
  39
  40 .br
  41      ---Dan   (this is the third line of the body)
  42 .EE
  43
  44 Each header field has a
  45 .IR name ,
  46 a colon,
  47 some
  48 .IR contents ,
  49 and a newline:
  50
  51 .EX
  52      Subject: Go, Bears!
  53 .EE
  54
  55 The field contents may be folded across several lines.
  56 Each line past the first must begin with a space or tab:
  57
  58 .EX
  59      Received: (qmail-queue invoked by uid 666);
  60 .br
  61              30 Jul 1996 11:54:54 -0000
  62 .EE
  63
  64 The field name must not contain spaces, tabs, or colons.
  65 Also, an empty field name is illegal.
  66 .B qmail-inject
  67 does not allow field names with unprintable characters.
  68
  69 Case is irrelevant in field names:
  70 .B subject
  71 and
  72 .B SUBJECT
  73 and
  74 .B SuBjEcT
  75 have the same meaning.
  76 .SH "ADDRESS LISTS"
  77 Certain fields, such as
  78 .BR To ,
  79 contain
  80 .I address lists\fR.
  81
  82 An address list contains some number of
  83 .I addresses
  84 or
  85 .I address groups\fR,
  86 separated by commas:
  87
  88 .EX
  89      a@b, c@d (Somebody), A Person <e@f>,
  90 .br
  91         random group: g@h, i@j;, k@l
  92 .EE
  93
  94 An
  95 .I address group
  96 has some text, a colon, a list of addresses,
  97 and a semicolon:
  98
  99 .EX
 100         random group: g@h, i@j;
 101 .EE
 102
 103 An address can appear in several forms.
 104 The most common form is
 105 .IR box@host .
 106
 107 Every address must include a host name.
 108 If
 109 .B qmail-inject
 110 sees a lone box name
 111 it adds the
 112 .I default host name\fR.
 113
 114 All host names should be fully qualified.
 115 .B qmail-inject
 116 appends the
 117 .I default domain name
 118 to any name without dots:
 119
 120 .EX
 121      djb@silverton  ->  djb@silverton.berkeley.edu
 122 .EE
 123
 124 It appends the
 125 .I plus domain name
 126 to any name
 127 that ends with a plus sign:
 128
 129 .EX
 130      eric@mammoth.cs+  ->  eric@mammoth.cs.berkeley.edu
 131 .EE
 132
 133 A host name may be a dotted-decimal address:
 134
 135 .EX
 136      djb@[128.32.183.163]
 137 .EE
 138
 139 RFC 822 allows mailbox names inside angle brackets
 140 to include
 141 .I source routes\fR,
 142 but
 143 .B qmail-inject
 144 strips all source routes out of addresses.
 145 .SH "SENDER ADDRESSES"
 146 .B qmail-inject
 147 looks for sender address lists in the following fields:
 148 .BR Sender ,
 149 .BR From ,
 150 .BR Reply-To ,
 151 .BR Return-Path ,
 152 .BR Return-Receipt-To ,
 153 .BR Errors-To ,
 154 .BR Resent-Sender ,
 155 .BR Resent-From ,
 156 .BR Resent-Reply-To .
 157
 158 If there is no
 159 .B From
 160 field,
 161 .B qmail-inject
 162 adds a new
 163 .B From
 164 field with the name of the user invoking
 165 .B qmail-inject.
 166
 167 RFC 822 requires that certain sender fields contain
 168 only a single address, but
 169 .B qmail-inject
 170 does not enforce this restriction.
 171 .SH "RECIPIENT ADDRESSES"
 172 .B qmail-inject
 173 looks for recipient address lists in the following fields:
 174 .BR To ,
 175 .BR Cc ,
 176 .BR Bcc ,
 177 .BR Apparently-To ,
 178 .BR Resent-To ,
 179 .BR Resent-Cc ,
 180 .BR Resent-Bcc .
 181
 182 Every message must contain at least one
 183 .B To
 184 or
 185 .B Cc
 186 or
 187 .BR Bcc .
 188 .B qmail-inject
 189 deletes any
 190 .B Bcc
 191 field.
 192 If there is no
 193 .B To
 194 or
 195 .B Cc
 196 field,
 197 .B qmail-inject
 198 adds a line
 199
 200 .EX
 201      Cc: recipient list not shown: ;
 202 .EE
 203
 204 This complies with RFC 822;
 205 it also works around some strange
 206 .B sendmail
 207 behavior, in case the message is passed through
 208 .B sendmail
 209 on another machine.
 210 .SH STAMPS
 211 Every message must contain a
 212 .B Date
 213 field, with the date in a strict format defined by RFC 822.
 214 If necessary
 215 .B qmail-inject
 216 creates a new
 217 .B Date
 218 field with the current date (in GMT).
 219
 220 Every message should contain a
 221 .B Message-Id
 222 field.
 223 The field contents are a unique worldwide identifier for this message.
 224 If necessary
 225 .B qmail-inject
 226 creates a new
 227 .B Message-Id
 228 field.
 229
 230 Another important field is
 231 .BR Received .
 232 Every time the message is sent from one system to another,
 233 a new
 234 .B Received
 235 field is added to the top of the message.
 236 .B qmail-inject
 237 does not create any
 238 .B Received
 239 fields.
 240 .SH "RESENT MESSAGES"
 241 A message is
 242 .I forwarded
 243 if it contains any of the following fields:
 244 .BR Resent-Sender ,
 245 .BR Resent-From ,
 246 .BR Resent-Reply-To ,
 247 .BR Resent-To ,
 248 .BR Resent-Cc ,
 249 .BR Resent-Bcc ,
 250 .BR Resent-Date ,
 251 .BR Resent-Message-ID .
 252
 253 If a message is forwarded,
 254 .B qmail-inject
 255 changes its behavior as follows.
 256
 257 It deletes any
 258 .B Resent-Bcc
 259 field (as well as any
 260 .B Bcc
 261 field);
 262 if there are no
 263 .B Resent-To
 264 or
 265 .B Resent-Cc
 266 fields,
 267 .B qmail-inject
 268 adds an appropriate
 269 .B Resent-Cc
 270 line.
 271 It does
 272 .I not
 273 add a
 274 .B Cc
 275 line,
 276 even if neither
 277 .B To
 278 nor
 279 .B Cc
 280 is present.
 281
 282 If there is no
 283 .B Resent-From
 284 field,
 285 .B qmail-inject
 286 adds a new
 287 .B Resent-From
 288 field.
 289 It does
 290 .I not
 291 add a new
 292 .B From
 293 field.
 294
 295 .B qmail-inject
 296 adds
 297 .B Resent-Date
 298 if one is not already present;
 299 same for
 300 .BR Resent-Message-Id .
 301 It does
 302 .I not
 303 add new
 304 .B Date
 305 or
 306 .B Message-Id
 307 fields.
 308 .SH "OTHER FEATURES"
 309 Addresses are separated by commas, not spaces.
 310 When
 311 .B qmail-inject
 312 sees an illegal space,
 313 it inserts a comma:
 314
 315 .EX
 316      djb fred  ->  djb, fred
 317 .EE
 318
 319 .B qmail-inject
 320 removes all
 321 .B Return-Path
 322 header fields.
 323
 324 .B qmail-inject
 325 also removes any
 326 .B Content-Length
 327 fields.
 328 .SH "SEE ALSO"
 329 addresses(5),
 330 envelopes(5),
 331 qmail-inject(8)