This email related error commonly occurs when a cPanel account is set up to not handle mail for a domain. This can be corrected by logging in to cPanel, clicking on MX Entry, and ensuring that Email Routing is set to Local Mail Exchanger for the domain in question.
Please note that this assumes that the DNS MX record is also pointing at this server. This means that the public internet knows that message for this domain should be directed at this specific server.
