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SMTP communication problem, 521 Syntax error - Exchange Server 2003

Recently, we did a huge server move which included a change in public IP of our E-mail server, even after registering our reverse DNS, we had issues sending to AT&T. I posted an E-mail to AT&T postmaster requesting an unblock for this errorcode.

There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<exchange2.broward-workforce.org #5.5.0 smtp;521 Syntax error>

AT&T postmaster has come back to tell me that theyre not blocking our e-mails, which leads me back to the 521 Syntax Error, Ive never seen anything like that in an error code before on the 5.5.0 error, what perhaps could be the culprit in this issue?

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kyodai

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David Megnin

ASKER

The MX server that is giving me the error message, exchange2.broward-workforce.org is actually my mail server, the MX records match with the public reverse DNS just fine. So there are no issues on my end of the spectrum, It unfortunately seems getting any information or help from AT&T is next to impossible. I'm at a bit of a loss if they're telling me they're not blocking me though it appears it, and all my MX records are fine.

Their relay servers show as

aln-mailrelay.att.net
scc-mailrelay.att.net

Now I am able to telnet to them just fine, however of course the problem remains I'm still unable to get through their servers. A sugggestion that had just been brought up to me is perhaps they're blocking me by Name instead of IP?

I guess the next step is continue to hound their postmaster until I get a straight answer?

David Megnin

ASKER

Yep, AT&T was blocking us. We just had to get ahold of the right person to get it resolved.

David Megnin

ASKER

Thank you.