Hello POakleaf,
If you're unable to add an email account when you go to Settings > Mail > Accounts, make sure you're entering the correct server information for the account.
Since this email address is not one of the automatic set up ones (Microsoft Exchange, Google, Yahoo, AOL, Outlook) you'll need to select Other and manually enter all of the server information. You can try looking up your accounts server info here: Mail Settings Lookup
You can also find additional info for setting up email accounts here: Add an email account
If you're still unable to add the email account, try adding one that automatically loads the settings (Microsoft Exchange, Google, Yahoo, AOL, Outlook) or contact your email provider to verify what information you need to enter to get it to work in the Mail app on your device.
Cheers!