Help Mail filter

Hi everyone.
I am using qmail with vpopmail to offer mail services to multiple virtual
domains. My mail client is sqwebmail. I want my users (virtual users) to be
able to filter mail messages. I tried MAILDROP which does not seem to work with
virtual maildirs, although it worked fine with real users on the system, but it
knows nothing about vpopmail.
Anybody got maildrop to work with qmail and vpopmail. If not, is there any
mailfilter package that work instead.