At first glance it looks interesting. I don't know if it interferes with the fact that our exim configuration already uses a .pl file, but the good news is we know that perl support is built-in .
I'll schedule it for SpamBlocker at some point in the future if its workable.
Warning: I've tried and failed at two prior attempts at integrating greylisting, probably because I didn't know what I was doing and didn't give it enough time.
Since we already have a perl script in our exim installation: /etc/exim.pl, instead of adding another perl_startup line you should probably use the already existing script.
Also consider using nolisting either in addition to or instead of greylisting; we already use nolisting and find that it blocks quite a bit of spam before we do anything else at all.
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