Sign In Links are being corruputed by Outlook / Microsoft Defender

Our Sign In Links are very long. We recently started getting reports that these links are becoming invalid when opening from Outlook.

These users get an error saying, "Due to an internal error, this web page cannot be loaded. We recommend you close this page."

There is some related discussion in this forum link: https://learn.microsoft.com/en-us/answers/questions/1332988/microsoft-defender-corrupting-urls-in-email

TL;DR;

• Microsoft Defender is altering long URLs in Outlook.

• The URLs are being wrapped with the SafeLinks wrapper and then truncated to 2084 characters, corrupting them.

Solution:

• Ask users to be on the latest version of Outlook Desktop.

• Try to reduce the length of the login link.

• Send the login link in text format, too, so users can copy it and paste it into the browser if clicking on the link doesn't work.