If we have activated “Inbox by Gmail” for our gmail account. The browser will automatically redirect our request to inbox.google.com instead of gmail.com.
If we visit gmail.com, the browser will load inbox.google.com by default.
We can use the following steps to revert back our default mail window to gmail.
Click the settings link from the left sidebar in the “Inbox by Gmail” page.
Click the “other” tab in the modal window which opened.
Uncheck the option “Redirect Gmail to inbox.google.com”
Now if we load gmail.com, the old gmail UI page will load.
At same, if we want to use the “Inbox by Gmail” we can directly visit inbox.google.com