Why do I need to turn off MailScanner for cPanel Software Support Analysts & Engineers to investigate my email-delivery issues?
MailScanner is a third-party solution neither created nor distributed by cPanel. It uses a completely different Exim configuration. Attempts at normal troubleshooting methods return messages such as these:
firstname.lastname@example.org cannot be resolved at this time: All deliveries are handled by MailScanner
Additionally, returning to cPanel's Exim configuration by turning off MailScanner frequently resolves the delivery issues. If this is the case for you, the issue is with the MailScanner configuration, and you should utilize support options for MailScanner.