postfix[error] :Sender address rejected: User unknown in virtual mailbox table [closed]

I install an application, that it needed smtp information for sending mail, I provide smtp user, password and host for that application, but when it tried to send mail this error had occurred in the application:

"SMTPRecipientsRefused: {'[email protected]': (550, '5.1.0 <[email protected]>: Sender address rejected: User unknown in virtual mailbox table')} ".

what should I do?

mail server log:

Apr 29 13:41:41 ns3 postfix/smtpd[30281]: connect from unknown[xx.xx.xx.xx]
Apr 29 13:41:41 ns3 postfix/smtpd[30281]: NOQUEUE: reject: RCPT from unknown[xx.xx.xx.xx]: 550 5.1.0 <[email protected]>: Sender address rejected: User unknown in virtual mailbox table; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<ns1.webmart.com>

If you need to know more information, let me know.

Postfix rejected unknown senders. Comment out one line in /etc/postfix/main.cf:

#smtpd_reject_unlisted_sender= yes

and your problem will be solved.