"In a different universe where Slack is incredibly successful over the next two years and 98 per cent of knowledge workers use Slack, it does matter to Microsoft because the relative importance of email is hugely diminished," Butterfield said in the interview.
Conversations in Slack happen in dedicated spaces called channels, instead of "a single overstuffed inbox" and it allows users to choose which conversations are most important -- and which can wait.
"If email becomes less important, then that whole $35, $40 billion-a-year collaboration productivity business unit is threatened," Butterfield was quoted as saying by The Verge on Tuesday.
In an interview with CNBC earlier this month, Butterfield said: "What we have seen over the past couple of months is that Teams is not a competitor to Slack."
"When Microsoft talk about the product, they never mention the fundamentals that Slack does, and it's been 3 plus years at this point that they've been bundling it, giving it away for free, and talking about us," Butterfield was quoted as saying.