My question was related to ispconfig and its support of the new courier authlib. As far as i understand it maildrop uses the courier authlib - in the previous version they directly used a mysql auth from maildrop.
No, thats not the case as maildrop auth is not configured separately. Maildrop uses the normal auth mechanism of courier and this is set at compile time by the maildrop package maintainer. ISPConfig configures only courier-authdaemon which is used as authentication source for all courier based applications incl. maildrop.
Take a look at the courier config files.