This is not a direct answer to your question at all, but rather a discussion point:
Why do you feel you need/want MySQL support in exim.pl? Is there something you can't do with flat files? Both exim and perl do very well with flat files, even big ones, and using MySQL could result in a hit against MySQL for as much as every email received, which cause a very high load on MySQL, perhaps high enough to bring sebsite speed down when run on the same server as websites (which is what DirectAdmin is made for).
Are there important enough reasons to use MySQL in exim.pl to override this? Or are you going to use MySQL only under rare enouigh conditions so receiving thousands of emails an hour, as our severs do, wont slow down your websites depending on MySQL?
Jeff