If you have many exim processes, the first place to check is: Admin Level → Mail Queue Administration
Check for any patterns in the sender or recipient addresses. Check the status of some of the message to see why they're in the queue.. if there is a common problem as to why they're in your queue (bottom textarea)
You can also get exim to create a stats page for you:
cd /var/log/exim eximstats mainlog > stats.txt less stats.txt
Check it to see where most of the emails are headed, either outbound or local.