Hello @user77336 ,   I'd advise reaching out to our Delivery team to see if they'd have any further insight on your specific situation, especially if this warning is showing with actual email sendouts and not un-authenticated test emails.   Beyond that, it'd come down to making sure your authentication is 100% exactly as it needs to be, and satisfies Outlook's expecations. Anyone not using Outlook is unlikely to see such an error message, unless there's an actual issue with how the authentication was setup with your domain. You may need to reach out to OL support, or see if your domain host would have any further insight (if applicable). ... View more