Step 1: Click on the given link to add Mailcastr extension to your system from Microsoft Edge.
Microsoft Edge Add-ons - mailcastr
Step 2: Click on "Get" then "Add extension"
Step 3: Sign in to Gmail with your desired account
Step 4: For activating Mailcastr, click on "Login now"
Step 5: Sign in again with the same email id and you will be redirected to your Gmail home page.