Important: This article applies only to Exchange 2016 accounts.  RPC/HTTP has been de-emphasized by Microsoft in Exchange 2019 and may not be included in future versions of Exchange, so disabling MAPI/HTTP for Outlook connecting to later versions of Exchange could cause Outlook to be unable to connect to the mailbox.

MAPI over HTTP is a new transport protocol used to connect Outlook and Exchange. There are some known issues when Outlook is connected using MAPI over HTTP:

  1. Outlook intermittent slow performance
  2. Error message Outlook is not responding
  3. Error message Outlook is trying to retrieve data from the Microsoft Exchange server

To check whether Outlook is connecting via MAPI/HTTP or RPC/HTTP use Outlook Connection Status. Press and hold CNTRL key and right-click the Outlook icon in the notification area, then select Connection Status

Outlook

In the Protocol column, HTTP indicates MAPI/HTTP used, RPC/HTTP indicates Outlook is connecting via RPC over HTTP.

Outlook

Note: If you are experiencing any of those issues, please make sure that Outlook is updated to the latest version.

If the Outlook is updated to the latest version and the issues are still ongoing you can disable the MAPI/HTTP protocol.  We suggest that this be done as a last resort, and only for users experiencing the issues.

To disable the MAPI/HTTP protocol in Outlook the following Registry key should be created on user's computer:

Important: For editing Windows Registry, administrator rights are required due to the impact that changes made there can have on the system.  Please perform it at your own risk.

  1. Open regedit
    Regedit
  2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Exchange and create the DWORD entry:
    MapiHttpDisabled
    RegEdit
  3. Modify the entry to have Value:1
    RegEdit
  4. Restart PC

To verify if the changes took effect, check the Outlook Connection Status again.