Change This Setting to Redirect Gmail to Google Inbox
If you are a fan of Google Inbox but sometimes switch to Gmail by mistake (when you click on a Gmail link or bookmark), you can turn on a setting that will automatically redirect you to your Inbox.
To proceed with setting up a redirect, go to your Inbox on your computer and click the main menu in the upper left corner. Scroll down to select Settings, then under Other, select the Redirect Gmail to inbox.google.com checkbox.
Then when you visit gmail.com or mail.google.com, you will be taken to inbox.google.com instead.
You can still access Gmail by going to your inbox, opening the main menu and scrolling down to select Go to Gmail. If you want to disable redirection, go to setting and just uncheck the box.
Redirect Gmail to Computer Inbox | Google support via Google operating system