Actually, it's not risky at all - as long as it's validated. I am indeed sure that it's faster, since I benchmarked it by trying it with several modules against a 20MB mailbox. Most of them couldn't handle the variety of date formats, as I'd already mentioned. The two that could were much slower than using 'date'.
As to the advice to change to maildir... thanks, but I absolutely despise maildir for a variety of reasons. I was actually looking for advice on the program design/methodology (although bug-killing is certainly welcome); if you have any comments about that, they'd be most welcome.
I hate storms, but calms undermine my spirits.
-- Bernard Moitessier, "The Long Way"