CPANEL mailbox common error Print

1. The mailbox opened on the CPANEL panel reports the following error when sending mail to the outside:
A mailbox sends an email to B mailbox and reports an error: SMTP Error (550): Failed to add recipient (No Such User Here).
Email B sends email to A mailbox and reports an error: Misconfigured PTR record
Reason: It is caused by the fact that your two hosts are activated in the same CPANEL panel. That is to say, if A domain name activates a host in this CPANEL panel, B domain name also activates a host, but B domain name is using an external Mailbox system, at this time, when the mailbox of A domain name sends an email to the mailbox of B domain name, this error prompt will be reported.