Outlook.com / Hotmail / Microsoft Delivery Issues

Update timeline

1. identified Feb 25, 2026, 12:44 AM UTC

   We are currently aware of intermittent delivery delays and bouncebacks when sending to Microsoft-hosted domains, including Outlook.com and Hotmail.com. This issue is not caused by our network or IP reputation. Microsoft has made a recent change to their mail classification system that is incorrectly flagging legitimate sending IPs as having reputation issues. This is a global issue affecting multiple email service providers, not just DuoCircle. What we're doing: We are in direct contact with Microsoft's postmaster team and have provided them with our affected IP ranges. IP delisting and reclassification is being handled on a priority basis. We are actively monitoring delivery rates and will update this page as the situation progresses. What you may experience: Some outbound messages to Outlook.com and Hotmail.com addresses may experience temporary delays, deferrals, or soft bounces. Messages are being queued and will be retried automatically. No action is required on your end. If you have specific delivery concerns, please contact our support team. We will post updates as we receive them from Microsoft.

2. monitoring Feb 25, 2026, 09:49 PM UTC

   UPDATE: Outbound SMTP Delivery Issues to Microsoft Consumer Domains (Outlook.com, Hotmail.com, Live.com, MSN.com) Status: Identified — Active Mitigation in Progress Severity: Major Updated: February 25, 2026 We are continuing to experience intermittent delivery failures and deferrals when sending outbound mail to Microsoft consumer domains including Outlook.com, Hotmail.com, Live.com, and MSN.com. Affected messages are receiving 451 4.7.650 responses citing IP reputation-based rate limiting. This is a widespread, global issue affecting email service providers, universities, healthcare organizations, and government mail systems worldwide — not just DuoCircle. Microsoft appears to have made a change to their inbound mail classification system that is incorrectly flagging legitimate, fully-authenticated sending IPs as having reputation problems. Key facts: Our sending IPs maintain clean reputations with no blacklist presence, complaint rates well below industry thresholds, and full SPF, DKIM, and DMARC compliance. Microsoft's own IP Delist Portal confirms our IPs are not listed or blocked, yet their mail servers continue to return reputation-based deferrals. This same issue is being widely reported across Microsoft's own support forums, the mailop mailing list, Reddit (r/sysadmin, r/proofpoint), and by other major ESPs including Zoho Mail. Affected organizations range from ESPs handling millions of messages to Estonian public libraries sending book reminders and South Korean journalists receiving government press releases. What we are doing: We are in direct contact with Microsoft beyond their standard support channels and have provided our full IP ranges for priority delisting and reclassification. We are actively managing our sending queues, throttling delivery rates, and rotating to fresh IPs where possible to maximize throughput during the disruption. Messages to Microsoft domains are being queued and retried automatically. What you may experience: Outbound messages to Outlook.com, Hotmail.com, Live.com, and MSN.com recipients may experience delays, deferrals, or temporary soft bounces. Delivery to all other mail providers (Gmail, Yahoo, corporate/hosted Exchange, etc.) is unaffected and operating normally. No action is required on your part. Queued messages will be delivered as Microsoft's systems normalize. We will continue to post updates here as the situation evolves. Want to read more - https://learn.microsoft.com/en-us/answers/questions/5786144/all-sending-ips-temporarily-rate-limited-(451-4-7 https://learn.microsoft.com/en-us/answers/questions/5778217/not-able-to-send-email-has-been-temporarily-rate-l https://www.reddit.com/r/sysadmin/comments/1ree93r/anyone_else_getting_rate_limited_due_to_ip/ https://www.reddit.com/r/mxroute/comments/1rekcfj/deliverability_is_our_thing_but_this_week_has/ https://www.reddit.com/r/proofpoint/comments/1rdn1qr/microsoft_email_domains_deferring_messages_from/

3. monitoring Feb 26, 2026, 12:00 AM UTC

   We are observing significant recovery in delivery to Microsoft consumer domains (Outlook.com, Hotmail.com, Live.com, MSN.com) beginning around 23:15 UTC on February 25. Current state: The majority of our sending IPs have resumed normal delivery to Microsoft consumer domains Overall delivery rate to OLC has recovered to approximately 90%, up from near-zero during peak disruption The S775 and S843 rate-limiting errors that were affecting our pool have largely ceased What to expect: Messages that were queued during the disruption are now being delivered Some recipients may receive delayed messages over the next few hours as queues drain A small number of deliveries may still experience intermittent deferrals as conditions fully stabilize We are continuing to monitor closely and will post a further update if conditions change. We are not yet marking this incident as resolved — we want to confirm stability over a longer window before doing so.

4. resolved Feb 26, 2026, 01:00 AM UTC

   Delivery to Microsoft consumer domains (Outlook.com, Hotmail.com, Live.com, MSN.com) has fully recovered. All mail queues have drained and pending messages have been delivered.