"Gmailify links your existing account to Gmail so that you get all the bells and whistles — spam protection, inbox organization and even Google Now cards based on your mail — without having to leave your current address behind. All you need to do is open the Gmail app, sign in to your email account(s), and enable Gmailify," informs Google.
Which features are available? Spam protection, automatic categorization, labels, better search with support for advanced search operators, travel and hotel reservations appearing automatically in Google Now, better mobile notifications and all the other Gmail features.
How does it work? You can link your non-Gmail address (Yahoo Mail, Outlook.com, AOL Mail, etc.) to an existing Gmail account or to a new Gmail account. "When you sign in to the linked Gmail address, you'll see your messages from the other email provider in your mailbox. You'll be able to read, reply, and organize them just like you do in Gmail." The Gmail app keeps everything in sync, so a read email will be marked as read in the original account, archived messages will be added to a new Archive folder, while Gmail labels will be treated like folders.