I update my software and my Mail account no longer works on my iPad or iPhone?

Email stopped working, receiving, sending

iCloud email :

Settings, your name, iCloud, turn off Mail, wait a few moments, then turn it on again.

Non iCloud email:

Settings, Mail, Accounts, tap on the account. Delete the account then after a few minutes add it back again.

If this is on cellular connections then manually update your carrier settings.

Manually update your carrier settings on your iPhone or iPad - Apple Support (IN)