SEDNA incident
Outbound Mail Delivery: Rejections for Some Microsoft 365 / Outlook Recipients
SEDNA experienced a major incident on August 13, 2026 affecting SEDNA - www.sednanetwork.com and SEDNA - Private Hosting, lasting 2d 9h. The incident has been resolved; the full update timeline is below.
Affected components
Update timeline
- investigating Aug 15, 2026, 11:15 AM UTC
We are investigating an issue affecting outbound email from Sedna to recipients hosted on Microsoft 365 and Outlook. Microsoft's anti-spam filtering is rejecting messages sent from a number of our outbound IP addresses, and senders are receiving bounce-back notifications (NDRs) for affected messages. Inbound mail is not affected, and delivery to recipients outside of Microsoft 365 / Outlook is unaffected. We will provide further updates as our investigation progresses.
- monitoring Aug 15, 2026, 11:26 AM UTC
We are monitoring closely and continuing to work with Microsoft. Any messages that bounced during the incident can now be resent.
- investigating Aug 15, 2026, 11:30 AM UTC
We are seeing further reports of outbound emails to Microsoft 365 and Outlook recipients being rejected. The issue is ongoing and our engineering team is continuing to work with Microsoft and our email delivery provider on a resolution. Inbound mail remains unaffected. Bounced messages were not lost and can be resent once delivery is restored.
- monitoring Aug 16, 2026, 08:15 AM UTC
We are monitoring closely and continuing to work with Microsoft. Any messages that bounced during the incident can now be resent.
- investigating Aug 16, 2026, 08:16 AM UTC
We are seeing further reports of outbound emails to Microsoft 365 and Outlook recipients being rejected. The issue is ongoing and our engineering team is continuing to work with Microsoft and our email delivery provider on a resolution. Inbound mail remains unaffected. Bounced messages were not lost and can be resent once delivery is restored.
- monitoring Aug 16, 2026, 11:10 AM UTC
Some customers are experiencing SPF bounces, this is a side effect of the mitigation and not a continuation of the issue. We are continuing to monitor closely before confirming full resolution. Any messages that bounced during the incident can continue to be resent.
- resolved Aug 16, 2026, 11:12 AM UTC
This incident has been resolved. Any messages that bounced during the incident can continue to be resent.