It should have been possible to do this with any one of:
fetchmail + procmail
Net::IMAP Perl module
Mail::Box::IMAP4 Perl module
But in reality, it took a little bit of several (Net::IMAP is woefully unprepared for primetime, so it's right out).
Here's what should work with just Perl:
#!/usr/bin/perl -w
# copyright 2004 gabriel rosenkoetter
#
# Reuse and redistribution, modified [...]