Reason for an email not working on an iPhone

The most common reason for an email not working on an iPhone is that the user's password is incorrect. Often, this issue is caused by an incorrect password. Once you have a new password, your iPhone will start to work properly again. If you're able to do this, you can now check whether your email has been hacked. This may be a simple hack to fix the problem.

See also - https://www.whatstodaynews.com/why-is-my-mail-not-working-on-my-iphone/