[Dovecot] iterate_query does not use userdb - mail_location not found

[dovecot at freakout.de]

Hi dovecot-comminity,

can't get iterate_query working. doveadm cannot find mail_location
which comes from userdb query. dovecot itself works fine with sql.
Whats wrong? please help:

 [root at glen exim]# /opt/dovecot/bin/doveadm search -A mailbox Trash savedbefore 90d
doveadm(uwe at mitmachnet.de): Error: user uwe at mitmachnet.de: Initialization failed:
                            mail_location not set and autodetection failed:
                            Mail storage autodetection failed with home=(not set)
doveadm(uwe at mitmachnet.de): Error: User init failed

dovecot.conf:
passdb {
  driver = sql
  args = /etc/dovecot/sql.conf
}
userdb {
  driver = sql
  args = /etc/dovecot/sql.conf
}

sql.conf:
driver = mysql
connect = host=much dbname=toarx user=exim password=xxxxxxxx
default_pass_scheme = PLAIN
password_query = select user as username, password, userdb_home, userdb_mail, userdb_quota_rule from vusers where email = '%u'
user_query = select user as username, userdb_home, userdb_mail, userdb_quota_rule from vusers where email = '%u'
iterate_query = select email as user from vusers

Cheers
Axel