Yammer is essentially a social network that’s entirely focused on your business. In order to join your business’s Yammer network, an applicant must have a working email address from your company’s domain. You can also create external networks to allow non-employees, such as suppliers and customers, to communicate with your company.
When you opt into Yammer as your default social experience in Office 365, Office 365 users are mapped to their existing Yammer accounts. This means that when you click Yammer from your Office 365 global navigation bar, you do not need to authenticate again. Office 365 users without existing Yammer accounts are taken to a streamlined sign-up and verification process.
To know more about the Yammer simplified login, click here.