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Updated on Jan. 5, 2021
Slack has restored most of its messaging service following a nearly five-hour global outage that left millions of users scrambling for communication alternatives.
Slack reinstated its service around 2:30 p.m. EST on Monday, except for its calendar feature and email notifications. The company had not determined the cause of the global failure as of Tuesday.
"We're truly sorry for the disruption today," Slack wrote in a statement on its status page.
The outage started about 9:50 a.m. EST, according to Downdetector. Slack released a statement nearly 25 minutes later confirming that users could not load channels or connect to the service. The company provided outage updates through its Twitter account @slackstatus and its Slack status webpage.
During the downtime, many Slack users complained on Twitter that they had to switch to email to communicate with colleagues. Slack has long touted itself as an alternative to email, especially after releasing its intercompany messaging product Slack Connect in June.
Technical support specialist Sebnem Uguz said her Chicago colleagues at the marketing firm Firefly had to email her team in Turkey to report Slack's troubles. Uguz soon discovered she also couldn't access the messaging app.
"It is the first business day of the year, so it was inconvenient for us to see it down," Uguz said of Slack. "We had a Google Meet call right after emailing each other and shared our updates."
Wayne KurtzmanAnalyst, IDC
Slack guarantees a 99.99% uptime per quarter for customers of its Plus plan. Customers who experience less than that much uptime get service credit.
Slack's outage comes on the heels of its announcement that Salesforce will acquire the company for $27.7 billion this year. Slack has more than 12 million daily active users.
"This is not the way Slack envisioned 2021 starting," said Wayne Kurtzman, an analyst at IDC.
Slack was partially down for more than 12 hours in 2019 but has had few outages in recent years aside from that. According to Kurtzman, Slack has a better uptime than some of its competitors.