[exim] Throttle delivery of email

I work with a church that sends 60,000 emails per year. This isn't a
huge number, however it's big enough that from time to time they send
a large number of emails to a few of the ISPs in town. This gets the
church put on the suspect list.

It seems like there should be a way to say "if we have delivered 50
emails to this IP address in last hour, hold what we have in the queue
and wait an hour before sending more emails"

Any ideas?