Enabling Multiple Sign In In Gmail

If you’d like to be able to sign in to multiple accounts in the same browser, you can enable the multiple sign-in setting. This will allow you to sign in to more than one account using the same browser session. You can only sign in to a maximum of three accounts at a time.

Your default account

If you use multiple sign-in, the first account you use to sign in during that browser session will be your default account for the rest of that session. If you visit other Google products that don’t support multiple accounts after you’ve signed in, you will automatically sign in to your default account for that product. If you sign out of any Google product while signed in to any account, you will be signed out of all your Google Accounts at once.

To enable multiple sign-in:

1. Go to the multiple sign-in settings page.
2. Sign in to your account.
3. Select On to enable the multiple sign-in feature and select the checkboxes to confirm that you understand how to use multiple sign-in.
4. Click Save changes.

You can check whether multiple sign-in is enabled, or disable the option for your account at any time, by visiting your multiple sign-in settings page. Also, if you have multiple sign-in enabled, a triangle should appear next to your email address in the top-right corner of the page.

To enable multiple sign-in on additional accounts:

Once you’ve enabled multiple sign-in for one of your Google Accounts, follow the steps below to enable multiple sign-in for additional accounts you would like to sign in to:

1. Sign in to a product that supports multiple sign-in, using an account that has multiple sign-in enabled.
2. Click your email address in the top-right corner of the page to expand the drop-down menu.
3. Select Sign in to another account.
4. On the page that opens, enter the email address and password for another account you wish to access, and click Sign in.

When using multiple accounts, you will have to sign in to these accounts using the multiple sign-in feature. You can not use shortcuts in a new window such as www.gmail.com to access additional accounts.[source]