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I have a strange problem with postfix. This first screenshot is captured by tcpdump on postfix. This one gave me "501 Domain must resolve" error.

I tried to connect manually, and enter information as captured on tcpdump on putty, but got different result.

Using putty, server responds as 250, Sender Ok

SMTP Server is MDaemon, and our mail server is Postfix

Any idea why it happened and how to solve it?

Thank you

1 Answer 1

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Most mail servers allow different behaviour depending on who is connecting. This can be based on IP. It doesn't look like you are connecting from the sending mail server that is having problems. So you might expect things to be different. Try connecting from that server. Then check the IP Shield feature of MDaemon.

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  • I don't have access to that Mdaemon, but I checked using telnet on mail server, and it was rejected even though my domain has correct ptr. I'll inform that mdaemon server owner.
    – prd
    Aug 30, 2013 at 9:27

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