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Saturday, November 5th, 2022 7:09 PM

Cannot email from my private domain exchange email server

​Cannot email from my private domain exchange email server.  This started recently.  ​
​Keep getting this reply: ​

​Remote Server at (2001:558:fd01:2bad::4) returned '400 4.4.7 Message delayed'​
​11/4/2022 3:27:27 AM - Remote Server at (2001:558:fd01:2bad::4) returned '451 4.4.0 Primary target IP address responded with: "554 found on one or more DNSBLs, see" Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was 2001:558:fd01:2bad::4:25'   ​

​I have gone through the process of removing block on ip address at and their reply is it is not being blocked.  I am also not on any spam lists, have what seem to be correct spf, dmarc, dkim records for my domain.   Thanks in advance.​

​I am a customer of comcast business class internet and have spent time with Tier II support on this issue.  ​

​A ptr record was added but that did not fix the issue.  They said it needs to be fixed at the Xfinity end.  I can't post question on their support board because I do not have Xfinity internet.​

Official Employee


62 Messages

5 months ago

@user_cae7a3 Thank you for taking the time to reach out to us here on our Xfinity Forums. I can definitely take a look at the account. It sounds like we may need to get a ticket open though. Please send us a DM with your full name and address to Xfinity Support. 


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