It has come to our attention that some email from the IP address of our secondary mail server (NC023) is being blocked at Outlook.com. It seems that only email sent to Outlook.com domains — e.g., outlook.com, hotmail.com, msn.com — is being blocked, but email sent to other domains hosted by Outlook.com is not being blocked. It’s unclear why the differentiation.
We do have an account with Microsoft for the purpose of monitoring reports about mail sent from our IP addresses to Outlook.com mail servers. However, although the account tells us that the IP address is blocked, it doesn’t tell us why or provide us with any statistics, as it does for our other IP addresses.
We have contacted Outlook.com to determine what is happening here, as this too is a situation we’ve never seen before.
