Slack brought its messaging platform back online Monday afternoon after a nearly five-hour outage knocked out service for millions of users on the first business day of 2021. The company restored core functionality by around 2:30 p.m. EST, though calendar integration and email notifications remained impaired, and the root cause had not been identified as of Tuesday.
What went wrong and for how long
According to outage-tracking site Downdetector, disruptions began around 9:50 a.m. EST. Slack confirmed the problem roughly 25 minutes later, acknowledging that users could not load channels or connect to the service at all. Updates were posted through the company's status page and its @slackstatus Twitter account throughout the day. In a statement, Slack apologized: "We're truly sorry for the disruption today." By Tuesday, engineers had not publicly disclosed what triggered the failure.
How businesses coped without Slack
The outage forced many teams to fall back on tools Slack has spent years trying to replace. Sebnem Uguz, a technical support specialist at marketing firm Firefly, said colleagues in Chicago emailed her team in Turkey to flag the problem, only for Uguz to discover she too had lost access. Her team ultimately held a Google Meet call to share updates instead. The irony was notable given Slack's positioning as an email alternative, reinforced by the June launch of Slack Connect, a tool for messaging between different companies.
Service guarantees and timing
Slack's paid tiers come with reliability commitments: customers on its Plus plan are guaranteed 99.99% uptime per quarter, with service credits owed if that threshold isn't met. Monday's incident followed a 2019 outage that left Slack partially unavailable for more than 12 hours, though the company has otherwise maintained a relatively strong reliability record. IDC analyst Wayne Kurtzman noted that Slack generally outperforms some competitors on uptime, but added, "This is not the way Slack envisioned 2021 starting."
Context: a pending acquisition
The outage arrived shortly after Slack announced that Salesforce would acquire the company for $27.7 billion, a deal expected to close later in 2021. Slack reports more than 12 million daily active users, making even a few hours of downtime disruptive for a large swath of remote and hybrid workplaces that depend on the platform for daily coordination.