.TH qmail-header 5
.SH NAME
qmail-header \- format of a mail message
.SH OVERVIEW
At the top of every mail message is a
highly structured
.BR header .
Many programs expect the header to carry certain information,
as described below.
The main function of
.B qmail-inject
is to make sure that each outgoing message has an appropriate header.

For more detailed information, see
.BR http://pobox.com/~djb/proto/immhf.html .
.SH "MESSAGE STRUCTURE"
A message contains a series of
.I header fields\fR,
a blank line,
and a
.IR body :

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

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

.br
     ---Dan   (this is the third line of the body)
.EE

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

.EX
     Subject: Go, Bears!
.EE

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

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

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

Case is irrelevant in field names:
.B subject
and
.B SUBJECT
and
.B SuBjEcT
have the same meaning.
.SH "ADDRESS LISTS"
Certain fields, such as
.BR To ,
contain
.I address lists\fR.

An address list contains some number of
.I addresses
or
.I address groups\fR,
separated by commas:

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

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

.EX
        random group: g@h, i@j;
.EE

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

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

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

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

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

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

A host name may be a dotted-decimal address:

.EX
     djb@[128.32.183.163]
.EE

RFC 822 allows mailbox names inside angle brackets
to include
.I source routes\fR,
but
.B qmail-inject
strips all source routes out of addresses.
.SH "SENDER ADDRESSES"
.B qmail-inject
looks for sender address lists in the following fields:
.BR Sender ,
.BR From ,
.BR Reply-To ,
.BR Return-Path ,
.BR Return-Receipt-To ,
.BR Errors-To ,
.BR Resent-Sender ,
.BR Resent-From ,
.BR Resent-Reply-To .

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

RFC 822 requires that certain sender fields contain
only a single address, but
.B qmail-inject
does not enforce this restriction.
.SH "RECIPIENT ADDRESSES"
.B qmail-inject
looks for recipient address lists in the following fields:
.BR To ,
.BR Cc ,
.BR Bcc ,
.BR Apparently-To ,
.BR Resent-To ,
.BR Resent-Cc ,
.BR Resent-Bcc .

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

.EX
     Cc: recipient list not shown: ;
.EE

This complies with RFC 822;
it also works around some strange
.B sendmail
behavior, in case the message is passed through
.B sendmail
on another machine.
.SH STAMPS
Every message must contain a
.B Date
field, with the date in a strict format defined by RFC 822.
If necessary
.B qmail-inject
creates a new
.B Date
field with the current date (in GMT).

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

Another important field is
.BR Received .
Every time the message is sent from one system to another,
a new
.B Received
field is added to the top of the message.
.B qmail-inject
does not create any
.B Received
fields.
.SH "RESENT MESSAGES"
A message is
.I resent
if it contains any of the following fields:
.BR Resent-Sender ,
.BR Resent-From ,
.BR Resent-Reply-To ,
.BR Resent-To ,
.BR Resent-Cc ,
.BR Resent-Bcc ,
.BR Resent-Date ,
.BR Resent-Message-ID .

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

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

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

.B qmail-inject
adds
.B Resent-Date
if one is not already present;
same for
.BR Resent-Message-Id .
It does
.I not
add new
.B Date
or
.B Message-Id
fields.
.SH "OTHER FEATURES"
Addresses are separated by commas, not spaces.
When
.B qmail-inject
sees an illegal space,
it inserts a comma:

.EX
     djb fred  ->  djb, fred
.EE

.B qmail-inject
removes all
.B Return-Path
header fields.

.B qmail-inject
also removes any
.B Content-Length
fields.
.SH "SEE ALSO"
addresses(5),
envelopes(5),
qmail-inject(8)