It appears that as of last week, Comcast is blocking email from at least two service providers: AWS and Digital Ocean. Bouncebacks return with "550 5.1.0 Connection is not being accepted at this time." This can be reproduced via a telnet session to the Comcast mail servers and the connection will return the error noted above after "MAIL FROM:".
- sending IPs are not blocked by Comcast (multiple hosts tested)
- sending domains are not blocked by Comcast (different domains have been tested)
- SPF/DKIM/PTR records are valid.
Any help would be greatly appreciated.
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