Slack’s complicated relationship with email, according to its IPO filing

Slack is going public.
Slack is going public.
Image: Reuters/Thomas White
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For years, Slack has been called an “email killer.” Founded in 2009 as an internal communications tool for the now-defunct gaming company Tiny Speck, Slack was created to solve the frustrations of the email’s isolated (and isolating) nature and its lack of transparency.

After its commercial debut in 2014, Slack quickly caught the attention of other businesses similarly looking for an evolution in office communications. Five years later, the San Francisco-based company boasts more than 10 million users and 88,000 paid customers in 150 countries. It has annual revenue of roughly $400 million, and today it filed an S-1, the regulatory document that is a precursor to an initial public offering. 

“The most helpful explanation of Slack is often that it replaces the use of email inside the organization,” the company notes in its S-1 filing.

But the relationship between Slack and email is turning out to not be that clear cut.

The word “email” is mentioned 33 times in filing—and not every reference has to do with taking over email. The S-1 notes that Slack has an advantage over email when it comes to collaboration, but also that the company depends on email for growth.

In short, the relationship between Slack and email is actually a complicated one. Here are all the different ways that email has been framed by Slack in its filing to go public.

1. Email is outmoded

As noted in the S-1, email consists of fragmented silos of information that are difficult for multiple people to access, leading to a proliferation of memos and meetings just to keep the entire team coordinated. Enter Slack, which keeps a record of conversations, data, and documents all in one place. It even allows new employees who are added to a Slack account to view the history of communication.

The filing suggests that Slack is more than an email replacement. “It is a new layer of technology that brings together people, applications, and data.”

2. Email is closed off

Unlike email, Slack was designed from the ground up to integrate with external applications and services. According to the S-1 filing, Slack has more than 450,000 third-party applications or custom integrations as of January.

3. Email is a competitor

Slack says its biggest competitor in the $28 billion communication and collaboration software market is Microsoft, but it also lists email providers such as Alphabet Inc. (Google) as well as smaller companies that specialize in email filtering and email-inbox organization.

4. Email is … a market opportunity?

Anyone who uses email is a potential Slack user, according to the filing.

5. Email is … needed for growth

Slack says it plans to increase investment in its relationships with leading email providers. Why? Because customers want it. For example, the e-commerce company Shopify has built an integration that allows its employees to access their company email accounts via Slack. And earlier this week, Slack announced that it would integrate with Microsoft and Google’s email and calendaring platforms.