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
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,
headerbottom, which tells PMDF to append the
header lines to the end of the message, and
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.
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
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,