To fix this issue in the Mails application, you should simply:

Evacuate the email that is giving the issue by going to Settings > Mails and afterward open the Accounts tab. Tap on the email you need to erase, discover the 'Erase Account' alternative at the base and affirm your activity.

Hard Reset your Gmail by holding down both the Power and Home catch for 10 seconds Let proceed to trust that the gadget will boot up.

Go to Settings > Mails and afterward open the 'Records' tab once more, tap on 'Include Account' and afterward include the old email address that you erased before.

Mood killer the gadget (pushing down the force catch and utilize the Power Off slider) and betray

This fixed the server personality mistake for me when seeing one of the messages I got in the Mails application.
https://www.quickfixnumbr.com/cannot-verify-server-identity-imap-gmail/