In the e-mail, which was addressed to "yahoos" and filed with the U.S. Securities and Exchange Commission, CEO Jerry Yang said the Yahoo board is still reviewing the deal and will "take the time it needs to do it right."
"Our board is thoughtfully evaluating a wide range of potential strategic alternatives in what is a complex and evolving landscape," he wrote in the e-mail, typed in all lowercase letters.
Microsoft made its unsolicited bid for Yahoo last Friday, offering to pay US$44.6 billion for the company, or 62 percent over Yahoo's closing share price Thursday. The deal would greatly expand Microsoft's search and advertising business and could help it to compete better with Google online.
Yahoo is understood to be lukewarm on the offer. The company hopes a rival suitor will emerge with a counteroffer, or that it can forge a deal with Google that will allow it to remain independent, according to Wednesday's Wall Street Journal newspaper, which cited unnamed sources.
However, analysts have said it is unlikely another company could match Microsoft's sizeable offer, and a business deal between Yahoo and Google could raise antitrust concerns because of Google's already dominant market position.
In the email, Yang thanked the Yahoo staff for staying focused on their work amid the turmoil. The company has hired "top advisors" to assist it through the process and is focused on maximizing value for its shareholders, he said.