The cloud software provider has been approached by another, unknown, buyer, and told Microsoft, which put in a bid of its own.
Salesforce, which has a market value of almost $50 billion, is working with two investment banks to determine a response to approaches, two of the people said.
It has the option of telling any buyer to go forth and multiply or working out a sale.
Microsoft isn’t in talks with Salesforce, and no deal is going to be quick. Microsoft has said that it might compete for Salesforce if it was for sale.
Salesforce shares spiked and were immediately halted for volatility on the news
Salesforce offers a leading position in CRM, software, as well as cloud computing — the delivery of business software and services via the Internet.
Microsoft sells its own customer management software, but lags behind Salesforce.
Microsoft last week set a goal of increasing annual revenue from its commercial cloud business to about $20 billion.
Oracle Chief Executive Officer Safra Catz said an acquisition of Salesforce would create disruption in the software market.
She declined to comment on whether Oracle was interested in buying Salesforce.
Salesforce was involved in strategic-alliance discussions with SAP last year and SAP has confirmed it is not thinking about a Salesforce bid.