Hello Alan. That explanation is hugely helpful and you are correct. Outlook for Android does not allow you to explicitly set a "default" account, as the client does as a desktop application. It simply "prefers" whatever account you add first, which, in your case, is the Microsoft 365 account. That should be enough to block ads, but there is obviously something else misfiring.
Your observation about the version of desktop of Windows 11 is correct as well. For Outlook desktop clients (even with lots of added third-party accounts), Microsoft does not show ads to subscribers. The app version for mobile seems to employ a different advertisement distribution process that is sensitive to both the account mix and mobile app behavior.
Now that you've done clearing your cache and doing a restart, here's a more surgical approach before doing a complete reinstall:
- Temporarily delete the Gmail and Sky.com accounts
- Only have the Microsoft 365 account on the app
- Start the app and watch ad behavior for 24 hours.
- If the ads don't reappear, reinstall Gmail and Sky.com but disable the inbox sync instead.
- This should keep them readily available when you need them, but will not trigger the ad logic.
If the ads do still show even with only the Microsoft account, you will have to do a complete reinstall:
- Delete Outlook
- Restart the tablet
- Reinstall the Outlook app and populate only the Microsoft account first.
- Ensure you get ad free behavior before re-adding your other accounts.
Hope this helps, let me know if have further questions.
Best regards,