Browse to Gmail, and find the double diamond shaped icon in the search bar at the top of your browser and click it.
If you are still having problems after you do that, try the below steps:
- Click the Chrome Menu icon on the browser toolbar.
- Select Options (Preferences in Mac and Linux; Settings in Chrome OS) > Under the Hood.
- Click Content settings.
- In the dialog that appears, find the “Handlers” section:
- Select “Allow sites to ask to become default handlers for protocols.”
- Click Manage handlers and Delete Gmail from Ignored protocol handlers
- Logout and Login to Gmail and click the small gray icon in the omnibox
- Select Allow Gmail to open email links