maildrop postfix problem

I configured postfix (master.cf) with the following statement:

maildrop unix - n n - - pipe
flags=DRhu user=vmail argv=/usr/bin/maildrop -w 90 -d vmail
${extension} ${recipient} ${user} ${nexthop} ${sender}

the main.cf looks like this:
....
transport_maps = mysql:/etc/postfix/mysql-virtual_transports.cf
maildrop_destination_recipient_limit = 1
maildrop_destination_concurrency_limit = 1
....

Mailtransport works ok for the domains or emailadresses in mysql
virtual transport table.
But i want to use the qutoa system of maildrop. I think I have to use
the mysql entension of maildrop. I use a patched version
(http://www.syscp.de/wiki/docs/Instal...ensionmaildrop) of
courier-mysql (with mysql) cause under debian the release of maildrop
has not been compiled with the mysql extension.
The configuration of the maildropmysql.config seems to be ok, cause I
can see queries of the maildrop agent in the mysql log file. The
problem is the condition clause: WHERE email = vmail. This comes from
the line in master.cf: ...maildrop -w 90 -d vmail... . But I have to
use this statement cause i use virtual mailboxes under the vmail
useraccount and maildrop needs a trusted user.

What can I do to get a correct sql query out of maildrop???

thanks, daniel