[Mimedefang] Discard by $Subject

[Paul Murphy]

> Why force acceptance of messages when one can reject them in 
> the MTA. Waste of cycles and time. Anyway the manpage covers 
> using MD to do the job if that is REALLY what you want.

We're specifically _NOT_ accepting the message - the whole point of
MIMEdefang is that it sits alongside Sendmail and is consulted at each step
of the SMTP process, so where your Sendmail local ruleset would be called
once the DATA part has been completed, MIMEdefang is handed the same contents
and asked whether to allow it - this is indeed rejection at the MTA.  The
difference in CPU use and time is minimal if you are already using
MIMEdefang, and in most cases, having Sendmail local rules applied on every
message and then also calling MIMEdefang is more wasteful than just using MD
up front.

I'd also suggest that Perl code is much easier to write, follow and debug
than Sendmail local rules.

Paul.