Ok, here's a weird problem.. for some reason, when an email account (pop/forward/whatever) is created, the associated files are not setup in the qmail/mailnames/domain/ directory.. plesk shows the address and info just fine, but any mail sent to the address bounces back like it wasn't there. And there is not a trace of it in the filesystem..

Any ideas?

Ok, that was weird. Somehow the permissions on the psa/admin/sbin/wrapper application were set wrong. It had the wrong group permissions. (Had to check against a working plesk box.)