Facebook has acquired Redkix to build better messaging features into its Slack competitor

Facebook has acquired Redkix, an email startup that combines email, messaging and calendar features into one app, the company said. Facebook made the purchase in hopes of building out its own communication features inside Workplace, the enterprise version of Facebook that it hopes to compete with Slack.

The social networking giant declined to say what it paid in the acquisition. Redkix has raised $17 million and has offices in both Silicon Valley and Israel.

It’s unclear how Workplace plans to integrate Redkix’s technology, although it makes sense why Facebook would want it. Workplace, which is used internally by Facebook employees, is a lot like the regular, consumer version of Facebook. That means it has features like messaging and groups, but not more traditional office features like email and calendars.

It’s still tough to tell where Workplace fits into Facebook’s broader plan, though. Facebook is primarily an advertising business, but it doesn’t sell ads inside Workplace — it sells subscriptions.

When Workplace first debuted in early 2015, the idea of a subscription business was intriguing. The hope was that it would provide Facebook with an alternative revenue stream. (Given Facebook’s slowing revenue growth, it’s still pretty intriguing.) But it’s unknown how well the service is performing. Workplace has 30,000 businesses using the product, which sounds like a significant number, but Facebook doesn’t share how many of those businesses are paying customers. And it doesn’t break out Workplace revenue on earnings reports, either.

For comparison, Slack, the incredibly popular messaging service valued at more than $5 billion, claims 70,000 paying customers, and is projecting $1 billion in revenue in 2018.

Facebook acquired Redkix’s talent and technology, which means some Redkix employees, including co-founders and brothers Oudi Antebi, CEO, and Roy Antebi, CTO, will join Facebook’s Workplace team. The Redkix app will shut down, a Facebook spokesperson said.

Update: David Marcus, the former head of Facebook Messenger who is now leading the company’s blockchain efforts, is a Redkix investor. Facebook’s internal policies stipulate that anyone with a conflict like this can’t work on evaluating a potential acquisition deal for their own investment, a spokesperson said.

This article originally appeared on Recode.net.