[Exim] .forward, script, limit

Hello!

We run Exim in cygwin to automatically process excel files, which users
sends to us ;-)
Script process each mail several minites.
Sometimes we receives about 20 messages in one time, this makes our
server overloaded.
Is there any way to force exim to not receive any mail before prevoius
mail is processed?
Or limit number of concurrent scripts, which Exim run from .forward?

Thank you!