How to suppress the Office 365 AutoDiscover redirect warning in Outlook 2016 for Mac

Applies to: Outlook 2016 for MacExchange Online

Symptoms


When Microsoft Outlook 2016 for Mac connects to an Office 365 account, Autodiscover is redirected from HTTP to HTTPS, and you may receive a warning message that resembles the following:

Outlook was redirected to the server Autodiscover-s.outlook.com to get new settings for your account user@domain.com. Do you want to allow this server to configure your settings?
https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml
Click Allow only if you fully trust the source, or if your Exchange administrator instructs you to.

When this warning message occurs, you may select Always use my response for this server and then click Allow in order not to be asked about this specific server again for this Outlook 2016 for Mac profile.

You or administrators may want to suppress the initial warning message. This article contains information about how to do this.

Resolution


Install the December 13, 2016 update for Outlook 2016 for Mac (version 15.29.0) or a later update, and then follow the steps to configure the Outlook 2016 for Mac Autodiscover redirect warning behavior when you connect to Office 365.

For information about this update or to download the Outlook update package, click the following articles:


  1. Quit Outlook if it's running.
  2. Open Terminal using one of the following methods:
    • With Finder as the selected application, on the Go menu click Utilities, and then double-click Terminal.
    • In Spotlight Search, type Terminal, and then double-click Terminal from the search results.
  3. Enter the following command in the Terminal window, and then press Enter.

    defaults write com.microsoft.Outlook TrustO365AutodiscoverRedirect -bool true 
  4. On the Terminal menu, click Quit Terminal.

More Information


The TrustO365AutodiscoverRedirect preference can be configured to use the following values:

Boolean Setting valueDescription
trueDon’t prompt for trusted Office 365 endpoints. Outlook defines what URLs are trusted and this is not configurable.
falseOutlook will use the default behavior which is to prompt when Autodiscover Redirects occur.
if value is not presentOutlook will use the default behavior which is to prompt when Autodiscover Redirects occur.