[Chapter 35] 35.7 Forwarding with Resent-Headers
Author: Bryan Costales & Eric Allman
Date: 1999-01-06T21:52:36Z

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| Chapter 35 Headers |

## 35.7 Forwarding with Resent-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.

Table 35.9: Known Resent-Headers
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.

### 35.7.1 Remove and Recreate the From: Header

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