Diagnosing e-mail issues is often a time consuming task. Having your e-mail address, especially a corporate domain, blacklisted on a private list is even more troublesome. Each vendor has its own process and Comcast has their own as well.
Reporting Blocked Email
While attempting to remove a client's e-mail system from Comcast's Blocked Email list or SPAM blacklist I found that their default site was inaccurate. Most searches at the time either failed to provide a link or provided the Xfinity link
http://xfinity.comcast.net/constantguard/Support/Submitting-Reports
If email is unable to be delivered to a Comcast.net email address, it's possible the sender's email provider is blocked as an anti-spam precaution for Comcast customers.
The error message the sender receives contains a URL. This URL links to an FAQ with valuable information regarding the issue and steps necessary to request removal.
Email administrators can submit the blocked IP address to the Comcast Security Assurance department to determine if the IP address is eligible for removal by completing the Blocked Provider Request Form. Requests submitted through this form are reviewed on a 24 X 7 basis
Click here for a detailed list of error messages and associated FAQ's
This above process leads you to several FAQ's or a Chat line with a support person. The support person will ask you several questions and then just provide the following link. Use this link to request removal from Comcast's blocked email list.
http://postmaster.comcast.net/block-removal-request.html
Reporting Spam Received from an IP Address on the Comcast Network
When reporting spam, it is critical that you include the email headers of the spam message.
Please do not forward the spam message: this will remove the email headers.
Once you have copied the full message headers from the spam message, paste the header into an email and send it to abuse@comcast.net.
If you find this information useful, please e-mail Firestone Technical Resources. This will let us know that we need to continue to keep this post active.