Mail doesn’t work

Are you trying to use an Apple Mail Account?

Did you make sure that you have all the details for the setup and followed all the steps mentioned?

Mail settings you might need from your email provider - Apple Support

Add an email account to your iPhone, iPad, or iPod touch - Apple Support

Two things you can try, to get your Mail account working again:

Force restart iPhone - Apple Support, you will not lose data by force restarting the phone.

Or log out of iCloud on your phone in the settings, restart the phone and log into your iCloud account again.

Did you check the Apple Status Page, if all Apple Services are working in your region?

Apple - Support - System Status

I just tried, and I can access my iCloud Mail Account, if I log into my iCloud account on my computer and open the Mail App.

Did you check, that on your phone in Settings/Password & Accounts/Accounts->iCloud/iCloud the option for Mail is enabled?

You should contact Apple Support about that, and ask them to look into your iCloud settings, to find the reason for that.

Good Luck!