Problems with Outlook on non AD joined computers

Hi

I have the strangest problem.

I currently have one MBX server (server A) and one CAS+MBX (server B) server. The last one is in a DAG, but there are no other servers in the group as the other one is being reinstalled.

Server A is only temporary, while I rebuild my DAG setup.

The problem only applies to computers that are not members of the domain, and only to mailboxes on Server B.

When trying to set up the profile I get the infamous

The action cannot be completed.  The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.

If I move the mailbox to Server A, it works.

If I try to set up the mailbox on a computer that is member of the same domain as the mail servers, it works.

No SSL problems with OWA.

Please help! I am in despair!