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I have setup postfix to send outgoing mail, It works fine for most of the cases except for some e.g duke.alumni.edu where it gives me a 450 error, even though the email address is valid.

This is the exact error I get Sender address rejected: Domain not found (in reply to RCPT TO command))

Any suggestions on how I can rectify this?

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What's the sender address (or more precisely the domain part of the sender address) your MTA is offering to duke.alumni.edu? –  joschi May 12 '10 at 7:06
it is customerservice@carsala.com –  Shiv May 12 '10 at 16:32
Domain might be wrong according to this URL: dukealumni.com/get-involved/support-daa/alumni-email-address (shouldn't it be alumni.duke.edu?) –  weeheavy Dec 9 '10 at 14:10

1 Answer 1

Just to check, neither a dig to alumni.edu nor to duke.alumni.edu gives any answer. An whois to alumni.edu also returns no match.

You are sure that the subdomain duke.alumni.edu is valid in your environment?

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