Email not sending from iPhone after account reinstatement

After what was probably an email hack I've deleted and reinstated my email account on both my Mac & iPhone. It works fine on my Mac but despite appearing in the sent box on my phone they aren't going anywhere? I've checked all the server settings numerous times and they are identical. My email provider is slightly baffled too so no idea what to do? Thanks

[Re-Titled by Moderator]

Original Title: Sent email....not sent