A user's Microsoft Exchange mailbox is migrated to Microsoft Office 365 from an on-premises or hosted Exchange environment. However, after the migration, the user's mobile device can't connect to Microsoft Exchange Online through Microsoft Exchange ActiveSync.
This occurs if the mobile device isn't automatically updated to include the location of the Exchange Online mailbox. The mobile device has to be redirected to the new mailbox server location.
Set up Exchange ActiveSync again on the mobile device so that you can get the latest version of Exchange ActiveSync. To set up Exchange ActiveSync, follow these steps, as appropriate for the device that you're using.
Windows Phone 7 devices
Do one of the following:
If this is the first email account that you have set up on the phone, tap the E-mail tile on the phone's home screen, and then go to step 4.
If this isn't the first email account that you have set up on the phone, swipe left from the home screen.
Tap Settings, and then tap E-mail and Accounts.
Tap Add an Account, and then select Outlook.
Enter your email address and your password, and then tap Sign In. Windows Phone 7 tries to automatically set up your email account. If setup is successful, go to step 7.
If your email account can't be automatically set up, tap Advanced Setup. You have to enter the following information:
E-mail address: This is your full email address. For example, email@example.com.
Password: This is the password for your email account.
User name: This is your full email address. For example, firstname.lastname@example.org.
Domain: This is the part of your email address after the @ sign. For example, contoso.com.
Server: For instructions about how to find your server name, see the "How to find the server name" section.
Select the Server requires encrypted (SSL) connection check box.
Tap Sign In.
When Exchange ActiveSync asks you if you want to enforce policies on your phone, tap OK. Policies let you set a password on your mobile device and use a remote device wipe to clear all data from your mobile device in case it's lost or stolen.
Windows Mobile 6.1 or 6.5 devices
On the Home screen, select Start, select ActiveSync, select Menu, and then select Configure Server. If you have not yet set up sync with Exchange Server, you receive the following message:
Add Server Source
Type your email address, make sure that the Attempt to detect Exchange Server settings automatically check box is selected, and then click Next.
Type your email address again in the user name field, type your Office 365 password, and then click Next.
In the Server address box, type m.outlook.com, and then click Next.
Note If Exchange Autodiscover is set up correctly for your email domain, you might not be prompted for this info.
When you're connected, you're presented with options for the kinds of items that you want to sync by using Exchange ActiveSync. To change available sync settings, select the check boxes for the kinds of info that you want to sync with Exchange Server, select Menu, and then select Settings.
To change the rules for resolving sync conflicts, select Menu, and then select Advanced.
Android and iPhone mobile devices
For more info about how to set up Android and iPhone mobile devices, see the following Microsoft Knowledge Base article: