outlook.com

Multiple folks over on the Mailop list are reporting that Microsoft OLC (Outlook.com/Hotmail/etc)’s IPv6 inbound mail servers are deferring inbound mail delivery attempts with “451 4.7.500 Server busy. Please try again later” errors. The fix seems to be to stop trying to send it over IPv6 and send the mail to any IPv4 MX record instead, and then your queues will drain successfully.What domains are affected? Likely all domains I’ve listed here as handled by Microsoft, and only if you send over IPv6, and only if the recipient domain is a Microsoft-hosted domain that has an MX record with a hostname that maps to an IPv6 address.If you’re sending mail using an ESP or CRM platform, you’re probably not affected by this. Big mail sending platforms, especially US-based ones, almost exclusively use IPv4 IP addresses, not IPv6.Why is this affecting mail over IPv6 only? Nothing has been confirmed, but I

Check it out! It looks like Microsoft has updated SNDS to provide a bit more info than they provided previously. In the “Comments” column, they’re now including snapshot counts of spam complaints received for that IP address at various points throughout the day.Where it says 10 complaints at 4:30 pm and 18 complaints at 4:37 pm, I think that means that eight complaints came in between 4:30 and 4:37. Might that be useful for folks looking to better identify which sends at which time are generating the most complaints?Note: It appears that the date/time in that comments field is when the complaint occurred, not when the campaign was sent. I’ve seen at least one example where that complaint date in the comments is a few days after the campaign send date. I suspect that could cause a bit of confusion.[ H/T: Mawutor Amesawu and Jennifer Nespola Lantz ]