 | Chapter 35 Headers |  |
| Chapter 35 Headers | |
Some mail-reading programs (MUAs) allow users to forward messages to
other users. For example, the mush(1) MUA forwards
the current message to the user named fred with the following
command:
message 1 of 3>m -f fred
Messages can also be forwarded with dist(1) from mh(1) and from within other MUAs.
When messages are forwarded, header lines that describe the
forwarding user must begin with the Resent- prefix.
When fred receives this message, he sees two similar header
lines:
From: original-sender Resent-From: forwarding-sender
When both the original From: and the forwarded
Resent-From: appear in the same header, the
Resent- form is always considered the most recent.
The sendmail program examines only a few header names to see whether a mail message has been forwarded. Those that it knows are listed in Table 35.9.
| Resent- form of | Header |
|---|---|
Resent-Bcc: | Bcc: |
Resent-Cc: | Cc: |
Resent-Date: | Date: |
Resent-From: | From: |
Resent-Message-ID: | Message-ID: |
Resent-To: | To: |
If sendmail finds any header with a name beginning with Resent-,
it marks that message as
one that is being forwarded, preserves all Resent-
headers, and creates any needed ones.
Whether the message is forwarded or not, sendmail compares
the sender envelope address to the address in the From:
header (or Resent-From: if present).
If they are the same, sendmail deletes the From:
(or Resent-From:). The purpose of this deletion
is to add the sender's full name (the $x macro; see Section 31.10.42) to the
address. If the envelope and sender addresses are the same,
it is safe to delete and regenerate those header lines.
If the message is being forwarded, sendmail recreates
the Resent-From: header; otherwise, it recreates
the From: header (see Section 37.5.113, -d31.2).
This recreation is useful because some old versions of mh(1)
added a From: header without the full name ($x).
It is also useful in mail client/server arrangements in which
all mail is sent to the server. Because that mail is sent with
the TCP delivery agent, no $x full name is added.
On the server the From: is discarded, and there
is a second chance to add the $x. However, this can happen only if the address in the envelope and the address in
the From: are identical. Since the address in
the envelope is surrounded with angle brackets, so must be the
address in the From: header. One way to ensure
that they are the same is by defining the From:
header with $g in angle brackets, as <$g> in the
client's configuration file.
|  | |
| 35.6 Headers by Category |  | 35.8 Precedence |