E-Mail and Xfinity Connect Help

[Scott30092]

Some emails sent to me are taking days to be delivered to my inbox. The delay is occuring within Comcast's email network as outlined by the SMTP headers below. In this example (of roughly 20% affected), SendLabs received the email on Fri 6/29 at 12:12 and didn't forward to mail.comcast until Sun 7/01 at 20:37. 

Can anybody elaborate on what's being done to resolve the issue?

Received: from imta19.westchester.pa.mail.comcast.net (LHLO
 imta19.westchester.pa.mail.comcast.net) (76.96.62.15) by
 sz0163.wc.mail.comcast.net; Sun, 1 Jul 2012 20:37:47 +0000 (UTC)
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    by imta19.westchester.pa.mail.comcast.net; Sun, 01 Jul 2012 20:37:48 +0000

Received: from Dynect (216.146.40.15) by mtaout-222-ewr.sendlabs.com id hu2qhm0ir00p; Fri, 29 Jun 2012 12:12:09 +0000
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Date: Fri, 29 Jun 2012 08:12:06 -0400

[steve-baker]

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Scott30092 wrote:

Some emails sent to me are taking days to be delivered to my inbox. The delay is occuring within Comcast's email network

Well, the delay isn't within Comcast's network, the delay is between Comcast and Sendlabs.

as outlined by the SMTP headers below. In this example (of roughly 20% affected),

20% of what? 20% of all your email, or 20% of what Sendlabs sends you? Are all emails from Sendlabs delayed? Are emails from other outfits also delayed?

SendLabs received the email on Fri 6/29 at 12:12 and didn't forward to mail.comcast until Sun 7/01 at 20:37. 

Can anybody elaborate on what's being done to resolve the issue?

It's hard to say what the issue is. Some possibilities:

Unlikely

Email is just getting "stuck" in the queue at Sendlabs due to some problem they're having.

There's an intermittent rDNS problem with Sendlabs.

There's something weird going on at Comcast that causes them to sometimes "tempfail" email sent to your address.

Less unlikely

There's an intermittent DNS problem with the domain of the Sender email address (probably the From: address). Comcast won't accept email if they can't confirm via DNS that the Sender is using a valid email domain.

My guess

Sendlabs is running up against Comcast's rate limits. Comcast uses a reputation based system that allows variable rates of delivery depending on the reputation of the IP address of the sender. Maybe Sendlabs is sending email from a "new" IP address that Comcast is treating as "unknown", which would have a lower limit.

Other

Dunno. I probably got it wrong, but the things I mentioned are things that could account for what you're seeing.

Received: from imta19.westchester.pa.mail.comcast.net (LHLO
 imta19.westchester.pa.mail.comcast.net) (76.96.62.15) by
 sz0163.wc.mail.comcast.net; Sun, 1 Jul 2012 20:37:47 +0000 (UTC)
Received: from mtaout-222-ewr.sendlabs.com ([216.146.33.222])
    by imta19.westchester.pa.mail.comcast.net; Sun, 01 Jul 2012 20:37:48 +0000

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Date: Fri, 29 Jun 2012 08:12:06 -0400

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[Scott30092]

Re "the delay isn't within Comcast's network, the delay is between Comcast and SendLabs.".

Technically, that's correct. As some of my delayed messages came through MessageLabs (not stated in my note) and Symantec refers to this service as anti-spam, my hasty assumption was that Comcast contracted out to several services to do inbound spam filtering. IF that were true, then I'd consider Symantec to be a part of Comcast's infrastructure and responsibility.

However, researching further since my note, it seems most likely that Comcast is simply rate-limiting some of these third-party email services. SendLabs is a email delivery gateway run by a company called Dyn (a few clients include Zoosk, Twitter, Twitpic).

The 20% referred to 20% of the emails I've received on my comcast.net email address over the last week.

Now that I know these guys aren't acting as front-ends for Comcast email, I'll just have to live with the fact that the big guys are doing what they can to play well together.

[steve-baker]

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Scott30092 wrote:

Re "the delay isn't within Comcast's network, the delay is between Comcast and SendLabs.".

Technically, that's correct.

That's correct, period.

As some of my delayed messages came through MessageLabs (not stated in my note) and Symantec refers to this service as anti-spam, my hasty assumption was that Comcast contracted out to several services to do inbound spam filtering. IF that were true, then I'd consider Symantec to be a part of Comcast's infrastructure and responsibility.

Comcast *does* utilize serveral anti-spam services, but they're blocklists and "spam content" services. They wouldn't account for the delayed messages you're seeing. As far as I know (and I know more about it than some Comcast employees), third party services would have nothing to do with delayed messages.

However, researching further since my note, it seems most likely that Comcast is simply rate-limiting some of these third-party email services. SendLabs is a email delivery gateway run by a company called Dyn (a few clients include Zoosk, Twitter, Twitpic).

You could be right.

The 20% referred to 20% of the emails I've received on my comcast.net email address over the last week.

That suggests that there might be something weird going on with your email address.

Now that I know these guys aren't acting as front-ends for Comcast email, I'll just have to live with the fact that the big guys are doing what they can to play well together.

No, something is going wrong somewhere. But Comcast is interested in keeping their paying customers, not playing footsie with one of their competitors.

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[ComcastJordan]

I checked just to be sure and there are no blocks or delays against Dyn's sending IP.  It is likely (as far as we can tell) the issue is on Dyn's side or in between us.