SAN FRANCISCO — Five years ago, Marc Benioff negotiated to sell Salesforce, the software company he co-founded in 1999 and has run ever since, to Microsoft. If the deal had gone through, he would have been richly rewarded — but, in the end, just another employee of the tech colossus.With Tuesday’s news that Salesforce was buying Slack for $27.7 billion, Mr. Benioff did something much more difficult. He is now set to directly compete against Microsoft, one of the world’s most valuable companies, in its own favored territory.Microsoft has been slugging it out with Slack in the pandemic-fueled rush to …
