Since updating my iPhone to 18 my email account does not receive emails?

Remove your present account in Mail and then enter it back in using the appropriate option. Since you didn't mention if it was a Hotmail or Outlook email, you would use the Outlook.com option. If all else fails and you still can't use Hotmail or Outlook there is always the Outlook.app on the App Stofre you can use for Microsft email address.