[Exim] how to limit number of simultaneous pipe delivieries?

Hello,

I've been trying to find the best solution to limit the number of
simultaneous
deliviers via pipe transport. In my case I can receive more than 100
messages in a minute which should be delivered via pipe, each pipe
taking about 10 seconds to finish.
As a result I get a lot of running processes, and system starts to run
low on memory.

So, can someone advise me on a way to limit the number of simulatenous
deliveries? I tried with ulimit (inserting a call to it in a rc.d
script, I'm running under Linux), but it didn't help.

--
Best Regards
Vladimir Ivaschenko
Francoudi & Stephanou Ltd