qmail-header(5)
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 follow
ing fields: Sender, From, Reply-To, Return-Path, ReturnReceipt-To, Errors-To, Resent-Sender, Resent-From, ResentReply-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 fol
lowing 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 qmailinject 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 MessageId field.
Another important field is Received. Every time the mes
sage 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-Mes
sage-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 pre
sent; 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.