Postmaster

This page was designed to address questions on the following topics:

What do I need to know to avoid blocks when sending to Comcast?
What are Comcast's outbound mail servers?
IP and host names for Comcast's outbound mail servers.
What are Comcast's mail delivery error messages?
An index of all Comcast's error messages resulting from failed delivery attempts.
What are Comcast's dynamic IP ranges?
A list of Comcast's dynamic IP space.
How do I get my IP block removed?
An automated way to remove many blocks. Please read the FAQs to ensure this is a block our form will remove.
How do I sign up for Comcast's feedback loop?
Requirements before signing up for Comcast's feedback loop program.

All policies and thresholds on this page are subject to change. This site will be updated when such changes are implemented.

Exchange servers and Comcast DNSSEC

02/10/2012

With the recent launch of the Comcast DNSSEC platform, and with other ISPs soon to follow, some Exchange server admins may notice intermittant delivery issues. These appear to be related how they determine DNS resolution and from which source.
We've obtained some information from Microsoft and their website that may help resolve the issue and have posted it to our help forums here.

SMTP Error Codes Information Updated

02/4/2012

We've revised our information concerning the various SMTP error codes senders and users may see when communicating with Comcast.net message systems.
These codes are documented at http://postmaster.comcast.net/smtp-error-codes.php.

Certified Email is being discontinued

02/03/2011

At Comcast, we take online security very seriously. We partner with industry-leading companies that provide cutting-edge security technology to ensure you have the best online experience. Whether it's spam reduction or helping to protect against viruses, phishing, identity theft and other online threats, we never stop strengthening our network protection.

We are writing to inform you that one of our partners, Goodmail, has ceased operations and will no longer be integrated within Comcast's services. However, we want to assure you that we will continue to provide the most comprehensive suite of online security and protection services available from any Internet service provider.

XFINITY Internet customers can visit Comcast.net/security to get the latest security software updates, news, tips and information to help keep you and your family safe online. Customers will also find information on how to download Norton Security Suite, activate Secure Backup & Share and other great services, all included at no additional charge with XFINITY Internet service.

What this means to you:
If you check your email through the SmartZone Communications Center on Comcast.net or xfinity.com, you may have noticed a Goodmail envelope icon next to emails from certain retailers, government agencies and financial institutions. This icon will stop being displayed as of 2/7/11. As always, we encourage customers to use email responsibly and use judgment when opening emails.and clicking on links within those emails.if they come from questionable sources.

New limit on recipients

07/20/2010

We've changed our policy on how many recipients can be addressed in a single email. Check out http://postmaster.comcast.net/avoidblocks.aspx for details.

Blocklist Removal Changes

08/26/2009

We've updated our blocklist removal process to include some limitations on the number of requests that can be made per day.

See postmaster.comcast.net/IPB-removal.aspx for more information.

Change log is live!

07/20/2009

Our new change log is up and running. Be sure to check back often and/or subscribe to our RSS feed to keep up to date on the latests news and policies for sending to Comcast.