How to disable Yammer's email notifications
After you log in to Yammer, you can edit your your profile and email notification preferences, for example. You will find your profile settings by clicking the wheel icon at the upper left corner.
In the Settings section, you can define your email notification preferences (Edit settings > Notifications). It's a good idea to disable most of the email notifications, as otherwise you'll receive too many.
If you use your email to reply to a message from a group, your answer will be posted to the group in question and not delivered to anyone's email.