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I have restrictions set up to block certain sender addresses. Why aren messages from restricted senders blocked as soon as the client issues the MAIL FROM command?

April 26, 2017addresses block blocked certain Messages sender senders

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I have restrictions set up to block certain sender addresses. Why aren messages from restricted senders blocked as soon as the client issues the MAIL FROM command?

1 Answer

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By default Postfix does not reject clients until after it receives the RCPT TO command. The reason is that some SMTP clients do not recognize that they have been rejected, and they keep trying to send the message, causing connections to last longer than they should and a log full of warning messages. Another advantage to the default is that you get complete information about the connecting client before rejecting the message. You can change the default behavior by setting smtpd_delay_reject = no.