e-pastiem nav nekāda sakara ar A ierakstu. pat, lai validētu e-pasta sūtītāju, pietiek ar mx ierakstu.

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postfix: reject_unknown_sender_domain
Reject the request when 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).

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