[exim] Ratelimiting by unique recipients number

Hello.

A question about ratelimiting senders. As I can see, ratelimit can
limit sending rate by counting number of commands or connections.
But is it posible to limit by number of unique recipients, as Gmail does?

http://www.google.com/support/a/bin/answer.py?answer=59797&topic=9202

If exim can't do this, probably there is some third party solution?
Thanks in advance for any ideas.

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Cronfy.