Postfix + Maildrop + MySQL anyone?

Hello all,

I have a small Debian server with Postfix 2.1.5, Courier,
Amavisd 2.2/Spamassassin 3 and MySQL 4.1. I use virtual mailboxes
with MySQL as backend. So far everything is working fine, Postfix
delivers the (filtered) mail to the virtual mailboxes and Courier
can fetch them just fine.

Lately I wanted to do some automatic processing with Maildrop,
however, I am unable to get it to work.

I compiled MailDrop 1.8.0 from source with MySQL support and I've
set it up in master.cf according to various tutorials on the net:

maildrop unix - n n - - pipe
flags=DRhu user=vmail argv=/usr/local/bin/maildrop -d ${recipient}

I also created a maildropmysql.config which should work with my
database layout.

But evertime a mail arrrives I only see "user unknown. Command
output: Invalid user specified." in the logs. Maildrop itself
does not log anything I can find, so I don't know where the
problem is. If I switch back from "virtual_transport = maildrop"
to "virtual_transport = virtual" in main.cf the mail is delivered
fine, but Maildrop is obviously bypassed.

The courier-authdaemon is running and working, so I was wondering
why I should compile Maildrop with MySQL support and use the
maildropmysql.config file. Shouldn't Maildrop use the courier
authdaemon instead?

Has anyone an idea what went wrong?

Frank