.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)