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Long of the short, my company was recently bought out. We set up an SSL tunnel between us and our parent company for ease of access and yesterday I setup a Conditional Forward in our DNS so we can resolve FQDN's on their side.

Last night, my Exchange server bounced a message saying delivery is delayed on an email I sent to someone at the parent company. My guess is because my Exchange is trying to resolve the MX using their DNS servers because of the conditional forward for their domain.

They're using Exchange Online for email hosting, so there's no server across the SSL tunnel to hit, and no MX record within their own DNS for their own servers.

Any idea how I might resolve this?

Can I do a 2nd conditional forward for the MX sending it to the Internet for resolution? I know I can't setup a zone as well as having the conditional. Not sure where to go with this.

Jeff Packard
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2 Answers2

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Exchange has settings to "Use external DNS" to look up mail flow destinations that can be enable per send connector. I would enable this feature, and that should allow Exchange to go around your conditional forwarder. You will need to set a property in the Exchange server for the external DNS server that you want to use, 8.8.8.8 or otherwise, and then enable the option on the connector.

Cory Knutson
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As first step I would do a NS lookup on your local MS Exchange server for there domain from the other company to check what you got here:

nslookup 
set q=mx

I have seen some setups where they had a local Exchange server (and for some reasons) a local MX entry pointing to the no longer existing Exchange server instead to the one in the cloud. The fix here was quite easy as a DNS cleanup solved the mess.

BastianW
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