In addition to returning messages, PMDF sometimes sends warnings
detailing messages that it has been unable to deliver. This is
generally due to timeouts based on the setting of the
notices channel keyword, although in some cases channel
programs may produce warning messages after failed delivery attempts.
The warning messages contain a description of what's wrong and how long
delivery attempts will continue. In most cases they also contain the
headers and the first few lines of the message in question.
PMDF will also optionally send a copy of all warning messages to the local postmaster. This can be somewhat useful for monitoring the state of the various PMDF queues, although it does result in lots of traffic for the postmaster to deal with.
nowarnpost are used to
control the sending of warning messages to the postmaster.
warnpost tells PMDF to send a copy of all warning messages
to the postmaster unconditionally.
PMDF to send a copy of the warning to the postmaster unless the
originator address on the as yet undelivered message is blank;
i.e., the postmaster gets copies of all warnings of
undelivered messages except for those as yet undelivered messages that
are actually themselves bounces or notifications.
errwarnpost instructs PMDF to only send a copy of the
warning to the postmaster when the notice cannot be returned to the
originator. No warning messages are ever sent to the postmaster if
nowarnpost is specified. The default if none of these
keywords is specified is to send a copy of warnings to the postmaster
unless warnings are completely suppressed with a blank Warnings-to:
header or a blank envelope From: address. Note that this default
behavior does not correspond to any of the keyword settings.