Microsoft Corp. has declared its widespread Microsoft 365 outage resolved, but ripples from the disruption continue to buffet email deliverability, prompting confusion among marketing platforms like Mailchimp. The incident, which peaked on January 22, 2026, affected tens of thousands of users across Outlook, Exchange Online, and related services in North America, leading to delayed messages and erroneous hard bounce reports from third-party SMTP providers.

According to the official Microsoft 365 Status account on X, posted at 06:29 UTC on January 23, the company confirmed: “We’ve confirmed that impact has been resolved. Full details can be found under MO1221364 within your Microsoft 365 admin center.” This followed hours of infrastructure struggles, with earlier updates noting traffic rebalancing and restoration efforts.

Outage Timeline Unfolds

Downdetector data showed spikes exceeding 15,000 reports on January 22, primarily for Outlook login and email access issues. CNBC reported users venting frustrations on social media, echoing a prior 21-hour downtime months earlier. Microsoft pinpointed faulty North American infrastructure, issuing error code 451 4.3.2 for temporary server failures, as detailed in Times Now.

By early January 23, CBS News noted Microsoft had restored services for thousands, with Downdetector graphs trending downward. A subsequent Microsoft 365 Status update at 05:33 UTC affirmed mail flow stability, though minor services required final tweaks.

Email Deliverability Disruptions Emerge

While core services recovered, outbound email from Microsoft 365 tenants faced scrutiny. The outage clogged Exchange Online queues, causing SMTP handoffs to providers like Mailchimp to register as hard bounces—permanent delivery failures—despite valid recipient addresses. Industry insiders report Mailchimp dashboards flagging these as bounces, triggering list purges and halted campaigns.

Posts on X from email ops professionals highlight the issue: Users described Mailchimp SMTP relays timing out against Microsoft’s recovering servers, generating false positives. No official Mailchimp statement ties directly to the outage as of 14:48 UTC January 23, but Downdetector’s real-time feed shows residual email complaints, with spikes in bounce-related searches.

Technical Roots of Bounce Surge

During peak disruption, Microsoft’s infrastructure rejected or delayed SMTP connections, per error logs shared in admin centers under incident MO1221364. This mimics hard bounces (5xx SMTP codes) to external relays. Tallahassee Democrat covered the broad impact, noting over 15,000 users hit basic functions. Recovery involved rerouting traffic, but transient rejects persisted into January 23.

Mailchimp’s system, reliant on real-time feedback loops, interprets these as invalid emails, a common pitfall in transient outages. Similar patterns occurred in past events, like the 2023 Exchange probe cited in historical Microsoft 365 Status posts, where mail flow lagged.

Industry-Wide Ripple Effects

Marketing teams paused sends, fearing reputation damage from bounce rates. People magazine quantified the scale: Tens of thousands reported issues, with Microsoft blaming North American infrastructure. SMTP providers beyond Mailchimp, including SendGrid and Postmark, likely saw analogous reports, though unconfirmed in current feeds.

Microsoft’s status page, linked in updates like this X post, emphasizes ongoing monitoring. As of now, primary services show green, but email pros advise checking bounce logs manually and whitelisting retries.

Microsoft’s Mitigation Steps

In the admin center, MO1221364 details load balancing fixes and infrastructure health checks. A USA Today article confirmed resolution for thousands, aligning with Reuters reports of restored productivity suite access. No ETA for full email normalization, but stability indicators suggest normalization within hours.

For Mailchimp users, best practices include suppressing recent bounces and monitoring delivery dashboards. The outage underscores SMTP fragility in cloud dependencies, prompting calls for better outage-aware retry logic in ESPs.

Looking Ahead to Stability

Microsoft’s pattern of rapid status updates via X and admin portals aided transparency, contrasting slower responses in prior incidents. CRN noted hits to Defender and Purview too, following Teams issues. Current Downdetector remains low, signaling broad recovery.

Insiders monitor for secondary effects, like delayed inbound mail or quota exhaustions from retries. With mail flow stable per latest posts, the focus shifts to purging false bounces and restoring campaign cadences.