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The feature, which has been present in the desktop version of Gmail for about a year, lets users sign into several Gmail accounts at the same time -- very convenient for those who often need to switch between one or more personal and business accounts.
To sign into another account, click on the account switcher at the bottom of the app's thread list. Then you can choose to either sign into an another account, sign out of all accounts, or switch between the accounts you've already signed into.
Other new features of note include a vacation auto-responder, which can now be set up from the mobile version of Gmail, and creating a special mobile signature that makes it clear you're responding to an email from a mobile device.