Comcast rate limiting

Russell from Port25 posted a comment on my earlier post about changes at Comcast.
Our (Port25) understanding is that Comcast is rate limiting such that they’re only accepting 6 recipients per second per sending IP.
This matches what I’ve been hearing from other bits of the industry over the last few days. I am recommending clients close the connection between each set of 6 email addresses.

AOL checking DKIM

Sources tell me that AOL announced on yesterday’s ESPC call that they are now, and have been for about a week, checking DKIM inbound. This fits with a conversation I had with one of the AOL delivery team a month or so back where they were asking me about what senders would be most concerned about when / if AOL started using DKIM. The other announcement is that AOL, like Yahoo, would like to...

Update on Yahoo and the PBL

Last week I requested details about Yahoo rejections for IPs pointing to the PBL when the IP was not on the PBL. A blog reader did provide me with extremely useful logs documenting the problem. Thank you! Based on my examination of the logs, this appears to be a problem only on some of the Yahoo! MXs. In fact, in the logs I was sent, the email was rejected from 2 machines and then eventually...

AOL and AIM mail

Earlier this week a question came up on a mailing list. The questioner recently started seeing an increase in rejections to @aol.com addresses. These rejections said <redacted@aol.com>: host mailin-03.mx.aol.com[] said: 550 We would love to have gotten this email to redacted@aim.com. But, your recipient never logged onto their free AIM Mail account. Please contact them and let...

Why do ISPs limit emails per connection?

A few years ago it was “common knowledge” that if you were sending large amounts of email to an ISP the most polite way to do that, the way that would put the least load on the receiving mailserver, was to open a single SMTP session to the mailserver and then to send all the mail for that ISP down that single connection. That’s because the receiving mailserver is concerned about...

DKIM "i=" vs "d=" and Reputation

This really should be part seven of a twelve part series or some such as it deals with an aspect of DKIM that’s really important, but is way down in the details of implementation. (dkim.org is a reasonable place to start for a general overview of DKIM). There’s an apparently endless thread on the DKIM-SSP spec development mailing list at the moment about the differences between two...

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