Resolved
Delivery to Microsoft-hosted mailboxes has been normal since 12:40 UTC. All delayed emails were delivered. This incident is resolved.
Monitoring
Delivery to Microsoft-hosted mailboxes returned to normal at about 12:40 UTC and delayed emails have been delivered. We are monitoring to confirm it stays that way.
Identified
We've found the cause. Emails to Microsoft-hosted mailboxes (Outlook.com, Hotmail, Microsoft 365) are being rate limited on the receiving side, and other email senders are seeing the same thing today. Emails are still accepted but some are delayed by several minutes while they're retried. Emails to all other providers are delivering normally. We're monitoring and will update when delivery times return to normal. If a code hasn't arrived, requesting a new one is the fastest workaround.
Investigating
We are seeing delays in email delivery for recipients on Microsoft-hosted mailboxes (Outlook.com, Hotmail, Microsoft 365). Affected emails, including one-time passcodes and verification links, may arrive late or require re-sending. Emails to other providers are delivering normally. We are working with our email provider to restore normal delivery.