Stewart Butterfield, co-founder and chief executive officer of Slack Technologies Inc., speaks during an event in San Francisco, California.

Business messaging service Slack briefed investors on Monday, as the company expects to go public with a direct listing on the New York Stock Exchange on June 20.

Slack provided updated information in an amendment to its initial public offering filing ahead of its pitch to investors. For the quarter ending April 30, Slack brought in revenue estimated between $133.8 to $134.8 million, up from $80.9 million in the same period a year ago. Slack's net loss expanded to about $39 million in the quarter, from $26.3 million.

The service, which primarily caters to businesses, said it has more than 10 million users as of January. In its briefing to investors, Slack said it will release first quarter earnings and host a conference call on June 10, as well as give a second quarter forecast.

Stewart Butterfield, co-founder and CEO of Slack, made the case that replacing email with Slack changes the way employees of a company communicate.

"This shift is inevitable. We believe every organization will switch to Slack or something like it," Butterfield said in a presentation.

He also pitched Slack as a software-focused company that believes the world is "only at the beginning" of its reliance on software. In that essence, Butterfield likened Slack as eventually becoming a utility, similar to the internet or electricity.

"The world is going to continue to use more and more software and we deliberately try to put ourselves in a position where Slack the company gets more valuable as the world uses more software because Slack the product becomes more valuable for our customers as that customer uses more software," Butterfield said.

Slack is the latest in a string of large technology companies coming to the public markets. But rather than a traditional IPO, the service will list its shares directly on the NYSE. It's the second major tech company over the last year to opt for a direct listing, following Spotify. Slack's ticker symbol will be SK.

Slack, similar to the recent IPOs of Lyft and Pinterest, will offer two classes of shares, to consolidate voting power among its top shareholders. Slack's Class A common stock will receive one vote per share, while Class B will be entitled to 10 votes per share.

Disclosure: Comcast Ventures, the venture arm of Comcast, is an investor in Slack. Comcast owns CNBC parent company NBCUniversal.