This is a common problem if you have your email hosted on a different server to your website. The main problem is the settings on the server that can be accessed via Cpanel.
Log into Cpanel and select Email Routing
Select the domain the email is not working for, then select Remote Mail Exchanger
It is usually set to Automatically Detect and that usually selects the Local Mail Exchanger option. That would be the wrong option if you host your emails for example with Gmail.