October 11, 2023 9:45am – We detected an increase in emails stuck in our queues that have not been successfully delivered.   After investigating, we’ve found that emails going to Microsoft 365 hosted emails are being delayed with a “Server Busy” message from the other side.   Downdetector is showing that users are reporting problems with Microsoft 365 services.

These emails are still “in line” to be delivered and once the issues at Microsoft are resolved, they should go through.   In the event that the emails are stuck for more than 4 hours, senders will receive a notification message indicating that there has been a delay but the message delivery will be retried for up to 5 days.   We assume that Microsoft will have the problem fixed by then.    We’ll post updates here as we have them.

Update  11:45am – Bleeping Computer has posted a story about the issue, saying it has to do with some new spam rules imposed by Microsoft.  Find the article here: https://www.bleepingcomputer.com/news/microsoft/exchange-online-mail-delivery-issues-caused-by-anti-spam-rules/   We can confirm that the error message mentioned in the article is what we are seeing in our logs.

Update 2:00pm – It looks like things have returned to normal.   We will continue to keep an eye on things, but all indications are that all backed up email messages have been delivered.