One particular user in our system is unable to connect to Exchange ActiveSync via her iPhone. When I try to connect using my own credentials on her iPhone it works (everything begins syncing), but when I input her credentials, the Settings app verifies the credentials are correct but nothing syncs. For example, if I open Mail, no items are shown. When I attempt to force a sync, it says "Cannot connect to server."
In Exchange 2010 Management Console the user is no different than the others. Exchange ActiveSync is set as "Enable" in Mailbox Features.
EDIT: Alternatively, if there is some easy way to create a new useraccount/mailbox and copy all of the contents of the old one over, I bet it would work, and that would be fine as well. She is a Mac user so we do not have to worry about her Active Directory account.
Okay the first thing to is to try https://testconnectivity.microsoft.com/
If a server error 500 occurs it might be related to the fact that the user is in a protected group, and thus some inheritance gets removed every hour..
From http://technet.microsoft.com/en-us/library/dd439375%28EXCHG.80%29.aspx
To check whether inheritance is disabled on the user:
Try also to remove the phone from the mail user.