PMDF System Manager's Guide

VMS MAIL only provides support for four message header lines: From:, To:, Cc: and Subject:. However, RFC 822 headers can contain many additional types of header lines. On OpenVMS systems, PMDF supports these additional header lines by optionally prepending or appending them to the message body whenever a message is delivered to a local user.

This behavior is controlled by the use of the headerinc, headeromit, and headerbottom keywords in the local channel block. The default is headerinc, which tells PMDF to prepend the header lines to the message --- this is the only one of these keywords supported on UNIX systems. On OpenVMS systems, the keywords headerbottom, which tells PMDF to append the header lines to the end of the message, and headeromit, which tells PMDF to strip all header lines, are also available.

Extreme care should be taken not to use these keywords on channels connecting to other message handling systems --- relocating or eliminating message headers violates RFC 821 and RFC 822 and can lead to serious problems. Note also that many seemingly "bothersome" header lines may contain valuable information required to decode messages, track down problems, or even authenticate who really sent the message and thus thwart attempts at forging mail messages.

The headerinc, headeromit, and headerbottom keywords will have no effect if they are specified in any channel block that does not use VMS MAIL or SMTP as its delivery mechanism, and indeed the headeromit and headerbottom keywords are only available on the OpenVMS version of PMDF. Their usage with SMTP channels should be limited to special SMTP channels; they should never be used with a TCP/IP channel such as tcp_local, etc.. Their usage with SMTP channels is intended for delivery of messages to local users on, for instance, microcomputers.