Is Slack overpriced now that the market knows Salesforce might buy it?

The Exchange is technically off today, but we're here anyway because there's neat stuff in the world of startups and money to talk about. So, let's yammer this morning about Slack's new valuation and what the market is telling us about what the venerable SaaS company is really worth.

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Recall that on Wednesday, news broke that Salesforce is considering buying Slack, a move that has potential merit and some question marks.

The merits could include bringing Slack's startup mindshare to Salesforce and bringing Salesforce's enterprise reach to Slack. In terms of questions, precisely how Slack fits into Salesforce's CRM-and-platform play isn't clear; Salesforce's own Slack-ish competitor, Chatter, hasn't taken control of its market in the 10-plus years since its release (here's TechCrunch covering its launch back in 2009), making the possible home of Slack inside Salesforce slightly suspect.

Still, Slack investors cheered the concept of Salesforce paying up for their company, while investors in the latter company knocked nearly $20 off its share price, perhaps worried about the very thing that Slack's owners were stoked to consider.

So, price. What's Slack worth? This is a question that's fun in both academic terms and also for understanding the current dynamics in the software M&A market - what do you have to pay to take a large chess piece off the software market's board?

Let's take a look at what we can learn from Slack's pre-news price, and its current, changed valuation.

What's it worth?

Here's a chart of Slack's value before and after the Salesforce news, just to give you a taste of how big an impact the reporting had: