Google recently launched it’s new Emailing app called “Inbox” but it seems to have limited it to people having invites only. Also, if you have an invite it’s not necessary that you will be able to invite more of your friends.
So, here is a way which you can use.
1. Take your friend’s email id and password whom you want to invite or who wants an Invitation from you 😉
2. Add his account to your device (Android Phone) and open his account .
3. Soon, you will receive a welcome email to Inbox from Google. Enjoy !!
P.S. Only people who got an invite can use this method to activate someone’s account , not your friend who’s account you activated using the above method.