[Exim] User Quotas

Hello,

Something I would love to do is to assign send quotas to users. By this I
mean something like no more than 200 messages an hour out from any given
account. It would just be a way of nailing someone misusing one of our
accounts quickly. So often the firt thing you know about a spammer is when the
queue gets suddenly rather too big (because most bought mail lists contain a
high percentage of duff addresses) or when the complaints starts hitting abuse.

I guess there would be a way through some sort of local SMTP proxy that
recognises local IPs and counts the mails with a certain "sender" address and
then refuses connections when the quota is reached.

Before I go down this path, I wonder if anyone has implemented anything within
exim that could do this?

--
Ian