Nigel Metheringham edited this page Nov 29, 2012 · 2 revisions
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I have one or two cases where my host correctly rejects messages, but the remote host is quite persistent, and keeps trying over and over.


It is an unfortunate fact that a number of SMTP clients, in violation of the SMTP RFC, do not treat a permanent error code that is given after the DATA portion of the transaction as a permanent error. Consequently they keep resending the message, and the worst offenders do so at very short intervals. The only way to stop such behaviour is to blacklist the IP address, or the envelope sender, or both, in such a way that future messages get rejected at RCPT time instead of at DATA time. You could also complain to the remote host's administrators.