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RIngman
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New Contributor

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3 Messages

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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3 days ago

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Comcast_Jorge

Official Employee

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57 Messages

4 days 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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RIngman

New Contributor

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3 Messages

3 days ago

So, I did a check on our firewall and it's using the correct public Outbound IP for SMTP/Port 25 traffic. I also verified with a couple of websites, that our PTR/Reverse DNS, SPF and SMTP HELO/EHLO are configured correctly.

I forgot to mention that has only happened with one eMail address so far. I don't believe it's an issue on their end though if you look at the Delivery Failure I mentioned. I just wanted to mention it due to being a very isolated issue with Mimecast and the IP listed on PBL.

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Comcast_Jorge

Official Employee

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57 Messages

 

Thank you for sharing those details, we are happy to work together on this and see if we can discover what the issue could be.  Can you please reach out through private message with your first and last name, full service address and account number or phone number? 

 

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3 days ago

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RIngman

New Contributor

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3 Messages

I tried to send you a Private Message, but you aren't showing up when I do a search to start one.

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3 days ago

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Comcast_Jorge

Official Employee

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57 Messages

Sorry for any confusion. Follow the steps here below:

 

• Click "Sign In" if necessary

• Click the "Direct Message" icon in the top right corner

• Click the "New message" (pencil and paper) icon

• The "To:" line prompts you to "Type the name of a person". Instead, type "Comcast Business" there

• - As you are typing a drop-down list appears. Select "Comcast Business" from that list

• - An "Comcast Business" graphic replaces the "To:" line

• Type your message in the text area near the bottom of the window

• Press Enter to send it

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3 days ago

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