Salesforce stock recently traded at $241.65, up 0.6%, compared with the the S&P 500’s 0.7% gain.
On Monday, the Justice Department had dropped an antitrust probe into the $27.7 billion takeover by Salesforce.
The DOJ's antitrust division opened a "second request" review into the deal earlier this year, as the Biden administration vowed to take a closer look at big tech mergers.
Last month, Slack reported fiscal-first-quarter revenue rose 36% from a year earlier to $273.4 million, with billings rising 35% to $278.5 million. Paid customer growth, the company said, was up 39% to 169,000.
Salesforce, which published quarterly earnings on May 27, boosted its full-year outlook to an adjusted profit between $3.79 and $3.81 a share and forecast revenue in the range of $25.9 billion to $26 billion.
"Considering the deal price and the presence of a robust competitor in the collaboration market in the form of Microsoft, (MSFT) - Get Report we expect investors to be keyed in on the early success Salesforce has in driving Slack penetration within its existing customer accounts," said Stifel analyst Tom Roderick. He carries a buy rating with a $295 price target for Salesforce stock.