How to suppress the AutoDiscover Redirect warning in Outlook for Mac
When you connect your Microsoft 365 account to Outlook for Mac, you may see a warning message that asks you to allow a server to configure your settings. This happens because Outlook redirects an AutoDiscover operation from HTTP to HTTPS. The warning message looks like this:
If you don't want to see this warning message every time you connect to your Microsoft 365 account, you can suppress it by following these steps:
Install the December 13, 2016 update for Outlook 2016 for Mac (version 15.29.0) or a later update. You can download the update from here.
Quit Outlook if it's running.
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.
Enter the following command in the Terminal window, and then press Enter:defaults write com.microsoft.Outlook TrustO365AutodiscoverRedirect -bool true
On the Terminal menu, select Quit Terminal.
This will prevent Outlook from prompting you for trusted Microsoft 365 endpoints. If you want to restore the default behavior of prompting when AutoDiscover redirects occur, you can use the same command with false instead of true.
For more information about this issue and how to modify the registry on Windows, see How to suppress AutoDiscover redirect warning - Outlook.
Why does Outlook redirect AutoDiscover operations
AutoDiscover is a service that helps Outlook configure your account settings automatically. It uses a predefined URL to connect to your email server and get the information it needs. For example, if your email address is firstname.lastname@example.org, Outlook will try to connect to https://contoso.com/autodiscover/autodiscover.xml.
However, some email servers may use a different URL for AutoDiscover. For example, Microsoft 365 uses https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml. In this case, Outlook will first try to connect to the predefined URL and then be redirected to the correct URL by the server. This redirection is done using HTTP status codes such as 301 (Moved Permanently) or 302 (Found).
When Outlook detects a redirection from HTTP to HTTPS, it shows a warning message to let you know that your account settings are being retrieved from a different website than expected. This is a security feature that helps you avoid phishing attacks or malicious websites that may try to impersonate your email server. You should only allow settings from sources you know and trust, or if your Exchange administrator instructs you to.
By suppressing the AutoDiscover redirect warning, you are telling Outlook to trust the Microsoft 365 endpoints and not prompt you again for this account. This can save you time and avoid confusion when you connect to your Microsoft 365 account. a474f39169