Problems with Invitations / Responds with Outlook

[Mailte90]

Baikal version: 0.10.1

Expected behaviour: Invitations to Outlook should have an E-Mail with accept / decline buttons. Responds (accept / decline) to Invitations coming from Outlook should send an EMail with the respond.

Current behaviour: Invitations to Outlook are empty E-Mails with an attachement called "not supported calendar message".
Responds to Outlook dont get send at all. Responds to other Mail Clients are working.