Update – Deliverability has made progress with the Microsoft team. Bounces are coming down. The initial find is the Microsoft spam algorithm incorrectly flagged IP addresses as “spammy” due to the mail stream increases beyond the threshold’s limits. We will continue to mitigate with them until all mail is flowing freely again.
Investigating – We are suddenly seeing high bounce rates coming from Microsoft accounts (hotmail.com, msn.com, outlook.com, live.com) tonight. Our deliverability team is currently in communication with Microsoft to determine the cause of this.