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Exchange Queue Stuck

Rick Ranck
Rick Ranck asked
We attempted to send a large amount of email out to our customers last night through our Exchange 2016 server. Everything went well except for a single queue, comcast.net. It sent the majority of the email out, however it is now stuck with the attached image. We have already restarted the transport service as an attempt to correct the issue. Any advice would be greatly appreciated.

Exchange Error Message
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Top Expert 2015

Are you sure the recipient's domain are valid?  Check and verify the MX using this tool.  Check a few of them.

IT Director
As it turns out, Comcast decided to block us again. The AI from their VADE spam filter decided that we should be blacklisted even though our SPF and DMARC records are all configured correctly. It took a bit of work, but I was able to get us removed and our email is now flowing as expected.