[exim] max amount of parallel deliveries

Hello,

i want to know if there is any possibility (which maybe i didnt found in
the specs) to limit the amount of parallel deliveries via a pipe transport.
The problem is that under some circumstances the OS cant deal with such a
high process count very well, without affecting the load of the system
itself.
For example File Descriptors or a not fast enough handling of all
deliveries which will end in constand increasing processcount and a memory
problem...