What Are the Top Requirements to Avoid Being Blocked When Sending to Comcast?
- Conform to the standards
All email must comply with all relevant RFCs.
- Ensure your rDNS is correct
Comcast performs an rDNS on the IP of the sending server. If the sending server does not have a PTR record and a MX or an A record set up properly the connections will not be accepted.
- Stay off DNSBL lists
Comcast employs several DNSBLs including Spamhaus Zen, TrendMicro MAPS, and ReturnPath's . Getting listed on any reputable DNSBL is likely to cause your email to be blocked.
- Keep your distribution lists clean
A large number of undeliverable emails sent to Comcast will get a sending IP blocked. All "Not Our Customer" NDNs should be treated as an unsubscribe request.
- Practice Good Abuse Management
Enforce AUPs and mitigate compromised accounts and machines. Dictionary / Directory Harvest attacks are treated seriously and will quickly lead to the sending IP being blocked.
- Keep it Static
Comcast does not accept mail from dynamic IP space. If email appears to be coming from dynamic IP space then it will not be accepted.
- Keep your IP reputation clean
Overall IP reputation is key to successful sending to Comcast. Ensure the overall sending reputation of the sending mail system is as clean as possible.
- Pay attention to error messages
Most non-delivery notifications Comcast returns contain links to FAQs which explain why the block occurred and instruct in how to remediate the issue. Take the time to review any errors; it is likely they hold the key to a quick remediation.
- Watch the sending limits
Comcast allows 10 simultaneous connections
Comcast allows 1000 recipients per message
Comcast allows a throttle rate based on your sender reputation and authentication
