Microsoft's Outlook.com is now giving users of its free email service the option of logging into Google Chat to exchange instant messages and engage in audio or video conversations.
The official tie-up has been a rare occurrence amid strained connections between the two technology giants.
With the latest addition, Outlook.com accountholders will have three different ways to interact with their friends and family in real-time discussions. They have already been able to use Microsoft's own Skype chat service and Facebook's messaging service.
Microsoft closed its Messenger chat service earlier this year as part of a switchover to Skype, which the company bought for $8.5 billion in 2011.
In a bid to direct more users to use the advertising-supported services that both the firms provide, Microsoft has introduced access to Outlook.com and Google Chat at no cost.
No ads are shown in live discussions on Google Chat, but marketing messages can be displayed if the conversations are saved, according to Google's policies. As it does with Gmail, Google's computers scan the context of the saved chats to help pick out which ads to show.
Microsoft believes it already has dented Gmail since it converted its Hotmail.com users and other email accounts operated under other domain names, such as MSN.com, to Outlook.com earlier this year.
"We do not have any queasiness about adding Google Chat," said Dharmesh Mehta, Outlook.com's senior director. "We think it's important to give people choice so they can make their email more personal. It also gives people one more reason to switch from Gmail to Outlook.com."
Washington-based Microsoft says it now has about 400 million Outlook.com users. That's up from about 360 million users of Outlook.com and the Microsoft's other webmail services three months ago.
Google, which is based in California, says it has more than 425 million Gmail users.
With inputs from agencies