Exchange 2010
Outlook 2007 and 2010
I have four users who share a departmental mailbox. User1 has his own mailbox; the other two do not. User1 and User2 can log into the shared mailbox in Outlook using their own Active Directory credentials. User3 and User4 cannot. User4 has tried both Outlook 2007 and 2010. They all have identical permissions to the mailbox (Full Access and Send As). They are all in the same OU as the mailbox. There are no error messages reported on the clients. The login box just blinks.
I had User4 log into a new computer so there would be a fresh local profile. I then created the Mail profile in Control Panel. It wouldn't take his credentials, but I hit cancel and it created the Mail profile anyway. Outlook still wouldn't open the mailbox under User4's credentials.
Any ideas why User2 can log in and the other two can't?