Yammer provides a more effective messaging system than email in several ways:
1) Messages on Yammer can be targeted to relevant recipients who subscribe to content rather than relying on reply-all emails that overload inboxes.
2) Yammer features threading to keep discussions manageable and transparent groups that employees manage themselves through a web interface rather than IT-managed email lists.
3) Content on Yammer is searchable and discoverable by colleagues, unlike emails trapped in individual inboxes, and Yammer does not have spam issues that plague email.