You already have a server side mail filtering script.
We techies call it an MDA and you wouldn't be
getting your mail without it. You probaby have either
procmail or qmail. qmail is weird because it doesn't know if it's an MDA or an MTA. Either one uses weird configuration syntax.
Here's a part of my spam filtering rule on this machine:
:0fw
| /usr/bin/bogofilter -e -u -p -WW -Ph -H
:0e
{ EXITCODE=75 HOST }
:0:
* !^X-Loop:
[email protected]
* ! ^FROM_MAILER
* ^X-Bogosity: Yes
spam_new/
:0 wf
* ^X-Bogosity: No
| sed 's@Subject:@Subject: ns:@'
Anyway, you need either someone who knows procmail to
configure a few rules for you, or perhaps you need a cgi programmer
to set up an interface that makes it easier to define your own.
I can set up a few rules for you right now if you give
me a call at 979-530-1300. I'll set them up as you are telling me
what you want so after a 5 minute phone conversation
they'll be done.
Just to qualify myself, I spent the day today installing and configuring
a complete sendmail and procmail based mail system
on a virtual server hosuing many domains. I was called in to do it because the client knew
I'd set up a far more robust system than what they got from Plesk.
If you would like a script to make managing your own filtering rules
easier I can help you with that too.