[exim] Process Overload

Recently my exim server has been running rampid on my server.

It queues up hundreds of messages for delivery and i see hundreds of

/usr/sbin/exim -Mc 1GxbzQ-0002Jw-0p

type messages in my process list.

The server load climbs to well over 150 across all three time intervals
-SIngle Processor, 2.4Ghz
-1Gb Ram server
My only recourse is to kill exim, delete the message queue and reload.

I have exim setup to block spam by comparing to multiple DNSRBL lists.

This only started happening a few days back and I cant get my finger on as
to why

Any suggestions?