OUTLOOK ISSUE – New Microsoft Direct Connect feature may prematurely connect Outlook to Office 365

SkyKick has identified the root cause of an issue related to a new Microsoft feature called Direct Connect. Some Partners have reported that customers have stopped receiving new email in their Outlook profile. 

This blog provides details on the issue - both how to avoid the issue and how to resolve it. We’ll post future updates on this issue here.

Affected customers

Customers with Outlook 2016 who are not yet active in Office 365, but have mailboxes provisioned in Office 365, may automatically connect to Office 365 before DNS cutover. When this occurs, emails continue to flow to the source, but because Outlook is connected to Office 365, the user will not receive them in their Outlook profile.


Starting in Outlook 2016 version 16.0.6741.2017, Microsoft enabled a new feature called Direct Connect to Office 365. It was designed to quickly connect Outlook 2016 to Office 365.

However, if Microsoft’s Autodiscover is not working on the source server or the connection between a computer and the source email server is interrupted, Direct Connect may cause Outlook to connect to Office 365 prior to cutover, even though the Autodiscover DNS path is still pointing to the source server.


  • End users will not see new email
  • Troubleshooting will be required to identify and resolve the cause of the source server connectivity interruption
  • Manual effort will be required to create a new Outlook profile
  • End users can use webmail to access email on the source server

How to avoid the issue with Office 365 Email Migration Projects

There are two workarounds that can be used to avoid this issue:

  • Registry Edit on each computer
  • CAS command in Office 365

Registry edit

A registry flag can be set on all computers with Outlook 2016 prior to provisioning mailboxes in the Office 365 tenant. This registry flag needs to be removed at cutover if you want to re-enable the Direct Connect feature once in Office 365. For more information, see Unexpected Autodiscover behavior when you have registry settings under the \Autodiscover key


  1. Go to Registry Edit on each computer
  2. Go to the following path: : HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover
  3. Set the Registry Edit: ExcludeExplicitO365Endpoint to Value : 1

Via Group Policy

You can also push these registry edits via Group Policy. For more information, see Outlook 2016 implementation of Autodiscover.

CAS command

A PowerShell command can be used in Office 365 to disable Outlook 2016 (MAPI) access to the mailbox. A corresponding PowerShell command will need to be performed at cutover to enable Outlook MAPI access at that time. For more information, see Enable or disable MAPI for a mailbox

How to resolve the issue with Office 365 Email Migration Projects

Direct Connect was designed to improve Outlook 2016 connectivity to Office 365. Unfortunately, an unintended negative impact of this feature requires a new Outlook profile be created for any profile that connects to Office 365 prematurely.

A new Outlook profile is required because the profile contains the MSExchMailboxGUID of the source server which is different from the MSExchMailboxGUID in Office 365. This mismatch corrupts the .OST for connectivity to both the source server and Office 365, resulting in the pop-up Temporary Mailbox Error.

There are two options to resolve the issue:

Option 1: Manually create a new Outlook 2016 profile connected to the source server. If you choose this option, follow these steps:

  1. Perform one of the workarounds described in this blog (registry edit or CAS command) to prevent the profile from connecting to Office 365
  2. Create the Outlook 2016 profile connected to the source
  3. At cutover, if you performed the CAS command, you must undo that command for the profile to connect to Office 365 at that time. (If you performed the registry edit, you only need to remove that edit to re-enable the Direct Connect feature once in Office 365.)

Option 2: Expedite the cutover and let the Outlook Assistant create a new Outlook 2016 profile in Office 365. Contact SkyKick Support to pursue this option.

We will continue to research and monitor this issue, and will provide updates as we learn more.

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Topics: MSPs For Partners Office 365 Outlook Assistant Office 365 Migrations