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RIngman
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Wednesday, November 11th, 2026 6:22 PM

Policy Block List (PBL)

Afternoon.

I tried sending an eMail and received the following delivery failure:

us-smtp-inbound-1.mimecast.com
Remote Server returned '<us-smtp-inbound-1.mimecast.com #5.0.0 smtp; 550 zen.mimecast.org Listed by PBL, see https://check.spamhaus.org/query/ip/68.54.211.122. - https://community.mimecast.com/docs/DOC-1369#550 [VVz2RrJzM3eVPkHPh_ReMw.us692]>'

We have been running our own eMail server for years now with a static IP on a Comcast Business account, so as far as I can tell we shouldn't be having an issue with being blocked.

It looks like maybe something isn't being routed correctly on Comcast's end as 68.54.211.122 isn't any of our static IP's.

Thanks,

Ryan

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19 hours ago

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Comcast_Jorge

Official Employee

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19 hours ago

 

RIngman Hello there, thanks for using our Forums and contacting us. I see you are having some issues with emails not going through and getting the error you shared. Since that isn’t one of your static IPs, we’d recommend checking the firewall/router NAT configuration and confirming which public IP outbound SMTP/port 25 traffic is actually using. Also verify the PTR/reverse DNS, SPF, and SMTP HELO/EHLO configuration for the intended static IP. If you continue to have issues let us know, and we are here to work with you. 

 

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