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

Original KB number:   3206915


When Microsoft Outlook 2016 for Mac connects to a Microsoft 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 to get new settings for your account Do you want to allow this server to configure your settings?
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 select 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.


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 Microsoft 365.

For information about this update or to download the Outlook update package, see:

  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 select 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 TrustO365AutodiscoverRedirect -bool true
  4. On the Terminal menu, select Quit Terminal.

More information

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

Boolean Setting value Description
true Don't prompt for trusted Microsoft 365 endpoints. Outlook defines what URLs are trusted and this is not configurable.
false Outlook will use the default behavior that is to prompt when Autodiscover Redirects occur.
if value is not present Outlook will use the default behavior that is to prompt when Autodiscover Redirects occur.