Comcastic SMTP Servers

One of our users complained that they did not receive a highly critical piece of email sent from a Comcast user. Other addresses on the recipient list at our company did receive the message.
Checking the logs we see that the recipients on the TO line of the email did not receive the message but recipients that were CCed did receive the message.
One of the mail admins has comcast so he logged in and sent him self a couple of test messages. Sure enough he received an error code 4.1.1. He tried again this time sending putting the his address as a CC and another address in the TO field. He was able to reproduce the users problem.
From googling, I see that some users were getting that error message when sending to certain domains back in February. It turned out to be a temporary problem for them. Not sure what that’s all about.