We are observing an elevated rate of spam foldering and open rates for messages destined to Office 365 domains

This incident has been resolved.

Summary: Beginning last week we made a change to add a URL to the list-unsubscribe header to be compliant with new rule “one-click” unsubscribe requirements from Gmail and Yahoo. After this update, some customers started reporting an increase in [new] junk foldering of messages destined to Office 365 addresses - it appears they were flagged by Microsoft’s Defender filtering framework. We worked with Microsoft who made changes to address this issue. In addition, some customers reported a large increase in opens and clicks on Monday and Tuesday of this week that we believe were caused by some action by Microsoft - likely a reclassification or redelivery routine.

Customers are reporting improvements and we continue to work with Microsoft on this issue. We will continue to monitor and we'll provide another update by 5 PM EST today.

We continue to communicate with Microsoft on this issue; they are responsive and are working on changes on their side; some customers are reporting improvements. We will continue to monitor and we'll provide another update by noon EST on Wednesday.

Microsoft have communicated to us that they have made updates to address these issues; customers are no longer reporting an uptick in opens.

Last week we rolled out a change to support the new list-unsubscribe header requirements for Gmail and Yahoo; this caused Microsoft to quarantine some messages for Office365 addresses; we are working with Microsoft on this issue. Some recipients are reporting receiving multiple copies of messages.