Postfix usercheck without LDAP, mySQL e.g.

Hello,

we want to use postfix as a mailrelay for many domains. In our case, we
cannot use a LDAP, mySQL e.g. database for the checking of exsisting users.

I´ve heared, that postfix supports this:
Postfix receives a new SMTP login. He receives the "RCPT TO:". Now he
holds the communication and make for him self a SMTP login to the
smarthost of the destination domain. Postfix waits for the output from
"RCPT TO:" (2xx or else). Postfix closes the connection the smarthost
and now he is able to granted or disallow the mail communication from
the other MTA.

I´ve heared, that this function is a simple command, but I did not found
it in my postfix book.

Does any one of you can help me?

Kind regards,

Carsten Remien

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