A mobile device can't connect to Exchange Online by using Exchange ActiveSync

Original KB number:   2427193


A user's mobile device can't connect to Microsoft Exchange Online in Microsoft 365 through Microsoft Exchange ActiveSync. However, the mobile device previously could connect.


This issue can occur for many reasons. These include, but aren't limited to, the following:

  • The device can't connect to the Internet service provider (ISP) or to the Internet.
  • The device isn't set up correctly.
  • The Exchange Online mailbox server that supports the connection isn't available because of maintenance or an outage issue.

Resolution - Step 1: Confirm that ActiveSync is enabled for the user

  1. Sign in to the Microsoft 365 portal as an admin.

  2. Select Admin, and then select Exchange to open the Exchange admin center.

  3. In the left navigation pane, select recipients, and then select mailboxes.

  4. In the list of mailboxes, double-click the user, and then select mailbox features.

  5. Under Mobile Devices, take the following actions:

    1. If you see Disable Exchange ActiveSync, this means that ActiveSync is enabled for the user. See Step 2: Confirm that the mobile device isn't blocked by an ActiveSync quarantine rule of this article.
    2. If you see Enable Exchange ActiveSync, this means that ActiveSync isn't enabled for the user. Select Enable Exchange ActiveSync, select Yes when you're prompted, and then select Save.
  6. After you re-enable ActiveSync, try to set up the device again.

Resolution - Step 2: Confirm that the mobile device isn't blocked by an ActiveSync quarantine rule

  1. In the Exchange admin center, select mobile, and then select mobile device access.
  2. Confirm that the user's mobile device isn't in the list of quarantined devices.

Resolution - Step 3: Confirm that ActiveSync can be set up by using Autodiscover

The Autodiscover service makes it easier to set up Outlook and mobile phones. The Autodiscover service uses a user's email address and password to automatically set up a user's profile.

To troubleshoot this issue further, run the Exchange ActiveSync Autodiscover test in Microsoft Remote Connectivity Analyzer. If the user is using a local wireless network to connect to Exchange Online, the user should run both tests to make sure that the local network allows for connections to the ActiveSync endpoints.

Test Exchange Online ActiveSync access externally by using Remote Connectivity Analyzer


Admins may want to guide users through running Remove Connectivity Analyzer if this is necessary. The Exchange ActiveSync Autodiscover test requires the users to enter their credentials.

  1. In a web browser, browse to the Microsoft Remote Connectivity Analyzer tool.

  2. Enter your Microsoft 365 sign-in credentials.

    Screenshot of entering your Microsoft 365 sign-in credentials.

  3. Select Perform Test, and then wait while the details pane is displayed.

    Screenshot of selecting Perform Test in the Remote Connectivity Analyzer window.

  4. Review the test results.

    Screenshot of Test Details in the Remote Connectivity Analyzer window.

  5. Take one of the following actions:

    • If the test passes, set up the mobile device.
    • If the test fails, confirm that the Autodiscover service is set up correctly. For more information, see the following resources:

Resolution - Step 4: Set up the mobile device without using Autodiscover (if you don't want to use Autodiscover)

We recommend that you use Autodiscover when you try to set up mobile devices. However, if you want to set up a mobile device without using Autodiscover, use the procedure that is described on one of the following Microsoft websites:

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

More information

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