* Cash-and-stock deal Salesforce's biggest-ever
* Mulesoft shares up 5 pct after market
* Including debt, deal valued at $6.5 bln (Adds analyst comment, details on deal value, background; Updates share price)
March 20 (Reuters) - Salesforce.com Inc said on Tuesday it would buy U.S. software maker MuleSoft Inc for about $5.90 billion in a cash-and-stock deal, illustrating CEO Marc Benioff's push to bolster the company's cloud-based portfolio with new technology.
MuleSoft shareholders would get $36 in cash and 0.0711 of a Salesforce share, or $44.89 per share, representing a premium of 36 percent to Mulesoft's Monday close.
MuleSoft shares were up 5 percent in extended trading after rising 27 percent during the day. Salesforce shares were down more than 2 percent after the bell.
Including debt, the deal was valued at $6.5 billion, the companies said in a joint statement.
"It is really a natural fit for Salesforce to own Mule," Steve Koenig, analyst at Wedbush Securities said.
"Salesforce usually helps customers move to the cloud and digitally transform their business that often starts with CRM, so having Mule helps eliminate friction as customers transform their business and to provide a more complete solution," he said.
MuleSoft listed on the New York Stock Exchange on March 17 last year at $17 apiece. It closed up 40 percent on the first day of trading, giving it a market value of nearly $3 billion.
Salesforce Ventures, the company's venture capital arm, led a $128 million funding round in MuleSoft in 2015.
Salesforce holds more than 18 percent of the global customer relationship management software market, followed by Oracle Corp with 9.4 percent, according to 2016 figures provided by research firm IDC.
MuleSoft makes software that provides enterprises with tools to automatically integrate various applications, devices and disparate data to help businesses networks run faster. It counts Coca-Cola Co, McDonald's Corp, Salesforce and Spotify among its customers.
Reuters had reported about the deal earlier on Tuesday.
BofA Merrill Lynch is Salesforce's financial adviser and Goldman Sachs advised MuleSoft. (Reporting by Supantha Mukherjee in Bengaluru; Editing by Shounak Dasgupta)