Can I limit messages per period of time per user?

[Jason Balicki]

Hello,

I'm only beginning this quest, so forgive me if this has
been covered (I've searched the mailing list and google
and come up with nothing.)

I am a sysadmin for a mortgage company.  As you're all
aware, sometimes mortgage loan officers send spam.  Well,
I won't stand for that on my watch, but recently I had
a scare.  We hired a new loan officer and the day after
he started I got a bunch of bounces from mail he sent
out the first day he was there.  I was livid at first,
but when I looked closer into the matter I found he had
simply sent messages to everyone on his personal mailing
list (that he typed in by hand (!)) telling them he had
changed jobs, "here's my new email address," etc.

Some of you may or may not know, but most mortgage brokers
are basically self-employed.  They get a percentage of the
loan and share it with the house for the facilities we
provide.  They do their own marketing.

When I was hired I created an acceptable use policy for
this network and in it it is stated that spam will not
be tolerated.

Now, background established -- how can I enforce this?
I block outbound port 25 on the firewall (among others)
so the only way mail is getting out is through our mail
server.  Is there a way that I can configure MailScanner
to only allow, say, 2 messages every 5 minutes per user?
(The numbers are arbitrary -- hopefully you get where
I'm going with this.)

Is this really something that should be configured in the
MTA?  I'm using postfix, and when I looked (granted, not
very hard) I couldn't find a directive that looked like
it would do this.  Could this be added to MailScanner, if
it's not already in there?  I know there would be a
performance hit, but for small companies (or large companies
with kick-ass mail servers) it might be worth it.

Any advice would be appreciated,

TIA,

Jason Balicki
Systems Administrator
Frontier Mortgage
St. Louis, MO