Many web messaging services, including GMail, identify the activation mail as Spam, and send it to your spam folder, instead of inbox.
If you are using GMail, follow these steps:
- Open your Spam folder:
 - Search your spam for a mail from 
genymotion-activation@genymobile.comwith subject "Welcome to Genymotion - User account activation": 
If you still don't find the mail, make sure that:
- Your mailbox is not full.
 - You spelled your email correctly when you registered.