Seems like after 11 pages some fix it and some are not. Maybe let me highlight some key takeaways:
1st situation - when you have hotmail or Microsoft mail account in your devices
Solution (1): Goto Setting > Mail > Accounts > Your hotmail or whatever Microsoft accounts > Delete and then reinstall
(note: choose outlook.com when reinstall)
Solution (2): Change the incoming server from smtp to pop
(note: your mails in device may disappear as it is what pop differs from smtp)
Solution (3): Make your hotmail inactive / disable the notification
(personally I doubt if this is a fix)
2nd situation - when you don’t have any hotmail account in your devices
Solution (1): Setting > General > Reset > Reset Network Settings > Reboot
(note: this solution is suggested by Apple help desk)
Solution (2): Goto Setting > Mail > Accounts > Your gmail or whatever mail accounts > Delete and then reinstall
Solution (3): Create a hotmail/outlook.com mail account, add it to your device and let your device update the certificate accordingly. You can remove the mail account afterwards.
Solution (4): Goto iCloud, logout and login again (some says it works but I don’t know the mechanisms)
Lastly, the issue is obviously caused by verification protocol between Apple and Microsoft, thus a permanent fix count on these two parties. Anyway I have filed a bug report via beta program. Let’s see.