aaPanel is operating on a host that must send mail from local applications. However, incoming mail is processed on a commercial mail server, represented by the MX records registered on the DNS, for the same domain.
In many configurations, Postfix will designate for local delivery any message with an address whose domain matches a domain assigned to the local host.
As suggested in an answer posted to a popular platform, local delivery may be disabled by the following configuration for Postfix:
mydestination = $myhostname, localhost.$mydomain, localhost
It is further suggested that a empty value for the setting would have the same effect.
In aaPanel, the configuration file shown for Postfix under Service Status, sets the value to empty.
However, messages with an address of a local domain are delivered locally, not to the mail server designated by the MX records in the DNS.
Why are the messages not being processed through the MX records, and how may the server instance on aaPanel be configured for such behavior?