I am the administrator for a system using shared hosting to host email services, and recently experiencing 5.0.0 failures with the error message below sending to comcast accounts: all hosts for 'comcast.net' have been failing for a long time (and retry time not reached) I suspect an IP block, but would like to confirm. Emails from this system tested successfully to reach other domains. I am an email administrator of another entirely separate system that DOES receive emails from this shared hosting system successfully. I can provide full headers of the succesful emails, if you need. Note: I am also an xfinity customer, personally, and emails from this system fail to reach my own comcast.net mailbox... so I can test as needed to determine if the issue has been resolved.
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