Outlook 2016 for Mac freezes on email folders that contain several encrypted messages

Original KB number:   3172627


In Outlook 2016 for Mac, when you navigate to a folder in which several encrypted email messages are displayed in the message list, Outlook freezes or experiences other performance issues.


To fix this issue, update Outlook 2016 for Mac to version 15.23 or a later version. Then, disable the preview feature for encrypted email messages by running a command in Terminal. To do this, follow these steps.

Step 1: Check the Outlook for Mac version number

  1. On the Outlook menu, select About Outlook.
  2. View the version number that is listed.
  3. If your Outlook installation is not at version 15.23 or a later version, install the June 14, 2016, update for Outlook 2016 for Mac or a later update. For information about this update, see MS16-070: Description of the security update for Office 2016 for Mac: June 14, 2016.

Step 2: Disable the preview feature

  1. Exit Outlook.

  2. Open Terminal by using one of the following methods:

    • Make sure that Finder is the selected application, select Utilities on the Go menu, and then double-click Terminal.
    • In Spotlight Search, type Terminal, and then double-click Terminal in the search results.
  3. Type the following commands in Terminal, and press Enter after each line:

    defaults write com.microsoft.Outlook DisablePreviewForSMIME 1
    killall cfprefsd
  4. Exit Terminal.

  5. Start Outlook.