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The more you know, the more you don’t know

This content is a little crusty, having been with me through 3 separate platform changes. Formatting may be rough, and I am slightly less stupid today than when I wrote it.
31 Aug 2009

Fix emails dropped or blocked by Comcast

As an email-based backup service, Fwd:Vault ran into spam filters pretty quickly. Most of this can be mitigated with proper server configuration and getting records in the right places (i.e. From there it’s simply a matter of reminding users to check the spam folder when things are missing. However through the tribulations of one of my testers, I found out that Comcast goes the extra mile for users of their webmail. Unlike most setups, where spam is simply redirected to a spam-specific folder, Comcast will delete the message outright, without issuing any kind of notice to the sender or recipient. Truly, above and beyond (belief). Of all the lousy IT practices I’ve seen over the years, this one takes the cake. No spam filter is perfect, so it’s guaranteed that they are dropping legitimate emails (case-and-point: I’m losing Fwd:Vault account emails). Plus it appears they default to a “highly suspicious” mode with newer systems, as, my IP address, and my DNS records are completely fresh and unblemished. Finally, the sheer size of their operation means that getting a hold of anyone to actually fix the problem when it happens to you is virtually zero. I’d go so far as to say that they can get away with this nonsense precisely because they are a large ISP. As a former “your company IT guy,” I can imagine getting at least an earful, and at worst a pink slip, if I were caught doing this. Despite my astonishment, I couldn’t deny reality. Through my logs I watched Fwd:Vault’s mail server find their systems, connect, and deliver the message and get a 250 response code (i.e. all good). Then over in my inbox I’d get exactly nada, ditto for the spam folder. Since the actual delivery had no technical issue, I had zero clue as to the cause of the problem. I wasn’t on any blacklists, the IP was static, and my DNS records were in good order, including a reverse DNS record with my hosting service. Fortunately, it seems that someone in the trenches at Comcast is fighting the good fight, as I took two long-shot attempts today and it seems one of them paid off. Here’s what I did, hopefully it works for you. 1. Use the feedback form at

I tried to retrace my steps on how I found this one, but their sites are so damn convoluted I kept going in circles. However I know I started from inside the web mail interface, aka their “SmartZone”. (See kids? That’s what we call irony. Can you say, “irony?") Whatever, here’s the link. You don’t need to log in to use the form: I selected Spam or Junk Mail in the checkboxes and wrote something to the effect of:

I am not receiving mail from in my Comcast email. I own and operate the mail server for this domain and have confirmed through my logs that the message is delivered properly (response code 250) to Comcast MX servers. My tests delivered via the server (IP It's been over 24 hours and I have not received a bounce, nor is anything showing up in my inbox or spam folder. As I have nothing else to go on, I am looking for help from your end.
I did not receive any reply, however I also took another step... **2. Use their RBL Removal Form**

This should only apply if your mail server has actually been blocked by Comcast, in which case you would likely see an error code of 550 in your logs. If your server picks up the full response from Comcast, you may also get additional helpful information as outlined in their list of custom mail delivery error codes. None of this applied to me, as the connection and delivery went off without a hitch. Still, I figured it was worth a shot; a bureaucracy this big is bound to have systems running into one another. I sent in a request to be removed from their RBL by way of this form: Most of the information will depend on your setup, however I did check the boxes for Implemented technology to filter or prevent transmission of spam and Changed the rDNS records to reflect a consistent and non-dynamic setting just in case. I included text similar to what I outlined earlier in the Issue Description box. I saw emails coming through less than 30 minutes after sending this message. However, I sent the feedback first, followed by a brief online chat with their support, who directed me to the RBL form. All told it was at least an hour between my first step and the delivered message. Update: I received this message back in response to my RBL request…

Thank you for contacting Comcast Customer Security Assurance. We have received and reviewed your RBL removal request. Below each IP address you submitted in your request, we have included the result of our research. Please do not reply to this message. **[IP address(es)]** We have received your request for removal from our inbound blocklist. After investigating the issue, we have found that the IP you provided for removal is currently not on our blocklist. We need the IP address currently blocked to further investigate this issue. The IP address is a number separated by decimals and is located in an error code starting with "550" in the returned email from Comcast. You can learn more about how to identify a blocked IP by visiting our Frequently Asked Question page at: Please verify the IP(s) and resubmit your request to

So it looks like the RBL request didn’t do anything. Unless it did, and some numb-nut at Comcast was covering for their idiotic policies. My gut tells me that I caught a particularly helpful support person manning the feedback desk who was able to punch the few keys it took to rectify the problem. If that’s the case, thanks for the help, and I hope the rest of you get to run into him/her as well. I sent the message around 2:00 pm on a Monday. You can find more helpful information, including a link to the Blacklist Removal Request Form, on the Comcast Postmaster Site. Best advice I can give: encourage your users to switch to Gmail. :)

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