Postfix - Sender address rejected: User unknown in virtual mailbox table
Sometimes you may want to be able to send email from non existent email addresses on your own networks for notification purposes, you may get error “Sender address rejected: User unknown in virtual mailbox table”. In order to over come this issue, you have to disable this option : “smtpd_reject_unlisted_sender”
Uncomment the following line in /etc/postfix/main.cf