Case 1: The iPhone user tries to setup Exchange mail in her new iPhone. She enters correct username and password, but it keeps popup with this message: Unable to verify the account information. After we check the settings, we find the restrictions was disabled. After enabling Restrictions, it starts working.
Case 2: The user's ActiveSync on the Exchange server was disabled. To enable it, open MC, navigate to Microsoft Exchange Permissive>Recipient Configuration>Mailboxes. Select the Mailbox you want to enable ActiveSync. Click on Mailbox Features and enable Exchange ActiveSync.
Case 3: The Account is disabled or the account is locked.
Case 4: The pass code policy is enabled in the Exchange. You must enable passcode on the devices.
Case 5: The password doesn't match.