NAME

       qmail-header - format of a mail message

OVERVIEW

       At  the top of every mail message is a highly structured header.  Many programs expect the
       header to carry certain information, as described below.   The  main  function  of  qmail-
       inject is to make sure that each outgoing message has an appropriate header.

       For more detailed information, see http://pobox.com/~djb/proto/immhf.html.

MESSAGE STRUCTURE

       A message contains a series of header fields, a blank line, and a body:

            Received: (qmail-queue invoked by uid 666);
                 30 Jul 1996 11:54:54 -0000
            From: djb@silverton.berkeley.edu (D. J. Bernstein)
            To: fred@silverton.berkeley.edu
            Date: 30 Jul 1996 11:54:54 -0000
            Subject: Go, Bears!

            I've got money on this one.  How about you?

            ---Dan   (this is the third line of the body)

       Each header field has a name, a colon, some contents, and a newline:

            Subject: Go, Bears!

       The  field  contents  may  be  folded across several lines.  Each line past the first must
       begin with a space or tab:

            Received: (qmail-queue invoked by uid 666);
                 30 Jul 1996 11:54:54 -0000

       The field name must not contain spaces, tabs, or colons.  Also, an  empty  field  name  is
       illegal.  qmail-inject does not allow field names with unprintable characters.

       Case is irrelevant in field names: subject and SUBJECT and SuBjEcT have the same meaning.

ADDRESS LISTS

       Certain fields, such as To, contain address lists.

       An address list contains some number of addresses or address groups, separated by commas:

            a@b, c@d (Somebody), A Person <e@f>,
               random group: g@h, i@j;, k@l

       An address group has some text, a colon, a list of addresses, and a semicolon:

               random group: g@h, i@j;

       An address can appear in several forms.  The most common form is box@host.

       Every  address must include a host name.  If qmail-inject sees a lone box name it adds the
       default host name.

       All host names should be fully qualified.  qmail-inject appends the default domain name to
       any name without dots:

            djb@silverton  ->  djb@silverton.berkeley.edu

       It appends the plus domain name to any name that ends with a plus sign:

            eric@mammoth.cs+  ->  eric@mammoth.cs.berkeley.edu

       A host name may be a dotted-decimal address:

            djb@[128.32.183.163]

       RFC  822  allows  mailbox names inside angle brackets to include source routes, but qmail-
       inject strips all source routes out of addresses.

SENDER ADDRESSES

       qmail-inject looks for sender address lists in the following fields: Sender, From,  Reply-
       To,  Return-Path,  Return-Receipt-To, Errors-To, Resent-Sender, Resent-From, Resent-Reply-
       To.

       If there is no From field, qmail-inject adds a new From field with the name  of  the  user
       invoking qmail-inject.

       RFC  822  requires  that  certain  sender fields contain only a single address, but qmail-
       inject does not enforce this restriction.

RECIPIENT ADDRESSES

       qmail-inject looks for recipient address lists in  the  following  fields:  To,  Cc,  Bcc,
       Apparently-To, Resent-To, Resent-Cc, Resent-Bcc.

       Every  message  must  contain  at least one To or Cc or Bcc.  qmail-inject deletes any Bcc
       field.  If there is no To or Cc field, qmail-inject adds a line

            Cc: recipient list not shown: ;

       This complies with RFC 822; it also works around some strange sendmail behavior,  in  case
       the message is passed through sendmail on another machine.

STAMPS

       Every  message  must contain a Date field, with the date in a strict format defined by RFC
       822.  If necessary qmail-inject creates a new Date field with the current date (in GMT).

       Every message should contain  a  Message-Id  field.   The  field  contents  are  a  unique
       worldwide identifier for this message.  If necessary qmail-inject creates a new Message-Id
       field.

       Another important field is Received.  Every time the message is sent from  one  system  to
       another,  a  new Received field is added to the top of the message.  qmail-inject does not
       create any Received fields.

RESENT MESSAGES

       A message is resent if it contains any of the  following  fields:  Resent-Sender,  Resent-
       From, Resent-Reply-To, Resent-To, Resent-Cc, Resent-Bcc, Resent-Date, Resent-Message-ID.

       If a message is resent, qmail-inject changes its behavior as follows.

       It  deletes  any Resent-Bcc field (as well as any Bcc field); if there are no Resent-To or
       Resent-Cc fields, qmail-inject adds an appropriate Resent-Cc line.  It does not add  a  Cc
       line, even if neither To nor Cc is present.

       If  there is no Resent-From field, qmail-inject adds a new Resent-From field.  It does not
       add a new From field.

       qmail-inject adds Resent-Date if one is not already present; same  for  Resent-Message-Id.
       It does not add new Date or Message-Id fields.

OTHER FEATURES

       Addresses  are  separated by commas, not spaces.  When qmail-inject sees an illegal space,
       it inserts a comma:

            djb fred  ->  djb, fred

       qmail-inject removes all Return-Path header fields.

       qmail-inject also removes any Content-Length fields.

SEE ALSO

       addresses(5), envelopes(5), qmail-inject(8)

                                                                                  qmail-header(5)