[otrs] No customer notifications sent

Hi all, I'm trying to setup an OTRS based ticketing system for my company (v2.4.4 on Windows 2003 SP2r2). I've already created some groups, roles and queues for testing purposes. I'm using my corporate AD as an customer & agent LDAP backend. Everything seems to work quite fine so far, except for the fact that no notification mails are being sent to the originator customer, Although all necessary properties are correctly retrieved from AD (including mail address). Also, logging does not indicate any mails being sent On the bright side: notifications to agents are being sent as expected as are (queue)responses to the customer. Hope anyone can help me out. Greetings, Yalu