Comcast troubleshooting support information

Sending successfully to Comcast and reaching the inbox is highly dependent on your sending reputation and following Comcast’s sending best practice guidelines. Please refer to Comcast's postmaster website for additional detail.

Troubleshooting tips

  • Check sending reputation: Look first at sending reputation metrics like complaints and spam traps. If sending reputation looks good, look at content, searching for anything that looks like phishing emails. If you have a good sending reputation, the spam decision is probably due to content.
  • Check for phishing characteristics in your email: Comcast uses Vade Secure as a factor in spam filtering decisions. 
    • Vade Secure looks at content in order to help identify phishing messages and other email scams. Any content that is similar to phishing emails (irrelevant or deceptive subject lines, excessive urgency, aggressive call-to-action, link redirects/shorteners, etc) will likely be the cause for spam filtering decisions.
  • Determine if all sending IP addresses are on Comcast’s complaint feedback loop: One of the common causes for deliverability problems at Comcast are high complaint rates and a low number of people marking your email as “not spam”. Low complaint rates and having subscribers marking your email as “not spam” signals to Comcast that you are less likely a spammer.
  • Determine if your IP address is present on the blacklists used by Comcast:
  • Check your SMTP logs for clues regarding the issue: Comcast blocks email with its own real-time block list. If your email is being throttled or blocked, check your SMTP logs for a response indicating a possible cause.
  • Review your list acquisition and  list hygiene processes: Spam traps are an important reputation measure for Comcast. When they add a new spam trap, they review it to ensure the address is not active in their system. All Comcast spam traps are at least three to five years old, so Comcast expects senders to not send to them.
    • Comcast deletes user email accounts after 12 months of inactivity. Ensure your win-back and suppression policies are set appropriately. Senders with longer selling or seasonal sending cycles may need to be more aggressive with win-back campaigns or with attempts to request updated information with inactive Comcast subscribers.
  • Determine if your email authentication is working properly: A misconfigured SPF or DKIM record can result in email being filtered or blocked.
  • Check your connection and throughput settings and SMTP error logs: Comcast will throttle your email if you are sending too much email to their servers. Reduce the connection and throughput settings if throttling occurs.
  • Check your retry settings: Increase the time between retries if still experiencing throttling issues. You may want to limit the number of retries per message to 2 or 3 temporarily if needed until you can isolate a cause of the deliverability problems.


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