In a nutshell: On Monday, IBM announced it would be using Slack companywide with its 350,000 employees. It's a feather in the cap for the communications startup, but the company still has an uphill battle. Slack Technologies continues to struggle with Microsoft Teams for marketshare, and shares have foundered since its IPO.

IBM has decided that Slack will become its official collaboration tool. The company has been using Slack with some internal team since 2014, but Business Insider reports the communications app will be rolled out companywide to its 350,000 employees.

In an SEC filing, the company points out that IBM has been its largest customer for several years. IBM will remain Slack’s biggest enterprise customer with over 350,000 installs, but the startup does not feel the need to change anything where financials are concerned.

Slack CEO Stewart Butterfield sees it as a milestone for the app’s usability.

“Going wall-to-wall in IBM — it’s basically the maximum scale that there is, so we now know that Slack will work for literally the largest organizations in the world,” Butterfield told BI.

Previously, IBM had Slack deployed to around 165,000 employees using its paid Enterprise Grid service. Its decision to expand to the rest of the company has effectively doubled its scale at IBM, although it is unclear if the expansion will be all paid accounts or a combination of subscriptions and free services.

The news is a boon for Slack in its battle with Microsoft Teams, causing stock in the company to rise more than 17 percent after Monday’s announcement. However, they trickled back down in late trading and continue to struggle to rise to initial public offering levels.

However, despite securing the rest of IBM’s employees, Slack still has an uphill climb against its rival software. Ever since the Redmond tech giant began including Teams in its Office 365 subscriptions, the companies have been at each other’s throats.

Last November, Microsoft reported Teams users had exceeded 20 million, surpassing Slack’s 12 million user base. The announcement sent its competitor’s shares tumbling 10 points. Slack claimed that Microsoft was padding its Teams numbers with voice call users, an accusation that Vice President Jared Spataro didn’t deny.

Masthead credit: NYCStock via Shutterstock