I have a user who is using Comcast email, and delivery was delayed about 40 hours for some reason. A message was sent on 7/26 at 3:42 PM and he didn't receive it until 7/28 at 7:31 AM. When I look at the "Email Delivery History," that email is confirmed as being successful at 7:31 AM. There is also an unsuccessful attempt with the response:
421 4.1.0 66.175.222.12 Throttled - try again later. Please see http://postmaster.comcast.net/smtp-error-codes.php#RL000003
So it seems as though Comcast is doing some kind of rate limiting based on the IP address of the originating server. Has anyone else observed this? Is there a way to tell Comcast not to rate limit emails from the groups.io servers?
Thanks,
David Walker
