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Exchange 2010 DnsConnectorDelivery

I'm having an issue with one domain. Mail is not being delivered to them from our server. Every test message sits in teh Queue with the "451 Primary target ip address responded with: 421 4.2.1 Unable to connect. Attempted failover to alternate host., but that did not suceed. Either there are no alternate hosts, or delivery failed to all alternate hosts."

I've tested the domain and done everything I can think of to get it to work. It's jmfinancial.net. I've seen a delay on the SMTP test, but nothing concrete. It's driving me nuts and of course it's a friend of our CEO. He's blaming our system because he can "get email fine from other people". I'm almost positive it's on his end, but I have no proof and I'm out of ideas. We can send and receive email fine to all other domains. We're not blacklisted and all of my Domain/MX checks return everything ok on our end. Any help would be greatly appreciated! We're running exchange 2010.

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jfletchster

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Sanjay Santoki

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jmchristy

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My server does resolve the IP address correctly, but I cannot telnet to it from the mailserver. I just says connection failed. I am however able to telnet to other mailserver from my exchange server. I just tested it with one of our customers. So, telnet is working, just not to their server.

Sanjay Santoki

Hi,

Furthermore, please be sure you have reverseDNS configured for your relay IP. That needs to be configured from ISP.

Thanks,
Sanjay Santoki

jmchristy

ASKER

I do have rDNS configured. It matches my SMTP banner as well. I'm not sure why it's not opening the connection to his mail server. I'm definitely able to contact other mail servers from my exchange box. His appears to be the only one that doesn't connect at all. I have an external XP machine that I am able to telnet into his mail server from. So, it's as though only my mailserver telnet is being dropped.

jfletchster

Do you have multiple external static IP's? Some routers/firewalls use all the external IP's as part of thier NAT pool, which can cause issues with sending email, as the router picks a different external IP at random for each transaction, causing the rDNS to fail. The way to check this it to get the server to do an External IP look up to a website a few time with a fresh browser each time and wait a few min in between each try.

jmchristy

ASKER

Update: It does appear to be something on their end. The owner isn't sure what it could be, and I'm not going to troubleshoot their issue. Thank you for the help!