[Exim] Tracking authentications

IS there a way to make Exim log who has authenticated? the reject log
shows failed authentications, but I want to track SUCCESSFULL
authentications also. I think that someone may have compromised one of
the servers I manage and it could only be done if the messages were sent
from the internal network or if the sender authenticated successfully.
So I want to track who authenticates ok so I can see if there's a
corilation of "user X authenticates, and 5 minutes later the Queue is
filled".

Thanks!
- --- Dan