The mail server does not accept letters, where to dig?

Question

MySQL

There is a server on freebsd with postfix, dovecot, mysql, nginx, rouncube installed.
With grief in half, I configured it to the state in which it sends mail to external domains, but when you try to send mail in response or just write a message to a mailbox on this server, a response from the server comes:

This is the mail system at host dataharbour.tk.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<[email protected]>: unknown user: "test"

Final-Recipient: rfc822; [email protected]
Original-Recipient: rfc822;[email protected]
Action: failed
Status: 5.1.1
Diagnostic-Code: X-Postfix; unknown user: "test"


---------- Пересылаемое сообщение ----------
From: "Макс Синюгин" <[email protected]>
To: [email protected]
Cc: 
Bcc: 
Date: Tue, 14 Mar 2017 12:02:51 +0300
Subject: otvet
otvet

the test user is created and mail is sent from it.
tell me in which direction to dig?

Answer 1

put yourself iredmail
Get a ready-made working mail system....

Answer 2

Look at the logs for what they say.

Answer 3

Are users virtual? Stored in mysql? If so, then most likely postfix cannot get the list of mailboxes.