Thanks Zhang, I appreciate your help. Unfortunately, I'm still confused.
Mail is sent to jeff@hong2.com - the MX for hong2.com goes to mailgun.com service for spam filtering
Mailgun.com forwards delivery to jeff@inbound.hong2.com - the MX for inbound.hong2.com points to my iRedMail server
But the message is never received in Dovecot/Roundcube. Postfix deletes it.
Sender address rejected: User unknown in virtual mailbox table; from=<bounce+f3ca76.809f-jeff=inbound.hong2.com@hong2.com> to=<jeff@inbound.hong2.com>
Is there a way to set up iRedMail to receive the message to jeff@inbound.hong2.com as having been delivered to jeff@hong2.com?
By the way, If I send from test@gmail.com directly to jeff@inbound.hong2.com, Postfix accepts the msg and delivers it. But when Mailgun delivers forward the msg to: jeff@hong2.com to jeff@inbound.hong2.com, it fails.
