[exim] Rate Limiting on Outbound connections

Hi All,

I'm looking for a solution to a problem - I have an MTA that accepts
messages for our middleware layer (its a mono app) - we've had a
couple of instances recently where we've had large amounts of mail
dumped onto our MTAs after an outage, exim has then pushed this into
the middleware layer at a rate faster than the middleware can handle
(mono, dont ask!).

I cant seem to find any elegant way to rate limit the outbound
connection from exim to mono? The only solution we've come up with is
another exim instance doing rate limiting on the inbound side before
handing off to the middleware layer.

Does anyone have any examples or suggestions for rate limiting the
outbound smtp connections??

TIA

D