Re: [SPAM] Re: Erzwingen von Fehler 550 an Stelle von Warnung 450

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http://www.postfix.org/postconf.5.html

reject_unknown_sender_domain Reject the request when Postfix is not final destination for the sender address, and the MAIL FROM domain has 1) no DNS MX and no DNS A record, or 2) a malformed MX record such as a record with a zero-length MX hostname (Postfix version 2.3 and later). The reply is specified with the unknown_address_reject_code parameter (default: 450), unknown_address_tempfail_action (default: defer_if_permit), or 550 (nullmx, Postfix 3.0 and later). See the respective parameter descriptions for details.

Ja, aber wenn der DNS einen temp. Fehler liefert, gibt auch Postfix einen temp. Fehler zurück...

Steht aber alles im Log.