This information is from a Comcast FAQ regarding bounced emails.
When I try to email a Comcast.net address I get a bounce back message with a 550 with a link to this page. What does this mean?
If you were directed to this FAQ via a link in an error message it is because you are sending mail from an IP address that is changing its Reverse Domain Name System (rDNS) frequently. Spammers often forge the rDNS of their connection in order to bypass spam filtering software. In Comcast's ongoing efforts to reduce the amount of spam that reaches our subscribers we must limit connections from an IP that may change its rDNS frequently in a set amount of time.
How do I fix this?
If you are an end-user, please contact your Email Provider or Mail Administrator for more information. If you are a mail administrator, please take this time to check systems for viruses or malware and make sure your rDNS is properly configured.
What is rDNS?
rDNS or Reverse DNS associates an IP address into a hostname or Domain name. For example, it might turn 192.0.2.25 (IP address) into "example.comcast.com" (hostname / domain name). rDNS does this by looking at the PTR record of the IP address in question and resolving it to a hostname based on the settings configured by a mail administrator. If your mail server does not have a PTR record set up to associate the IP address with the domain name, it will fail the rDNS test and the mail server will not be able to send email to Comcast.net. If your IP address connects with a different rDNS multiple times, your mail server will be blocked from sending to Comcast.net.
I am not a spammer, so why is this affecting me?
This block has nothing to do with the actual content of the email message. However, spammers often use valid, but forged DNS entries when sending email to avoid detection. However, Comcast does acknowledge that non-spam email may originate from misconfigured email servers and in some rare cases, virtually hosted servers. Please contact your Email Provider or Mail Administrator if you have specific questions about your mailserver configurations. Once reverse DNS is applied to your mail server or your system is cleaned of viruses, please submit a request to
http://www.comcastsupport.com/rbl to be considered for removal. To expedite review of your request, please include the error message sent to you and the specific IP address of the mail server that you believe is blocked in the body of the email. Please note: your mail server is not blocked from sending email to the cable.comcast.com domain.
Could rDNS be the problem?
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