Now available on the App Store, the latest iteration of Mailbox adds support for iCloud and Yahoo Mail accounts. While iCloud and Yahoo Mail are the most likely alternatives to Gmail, I am surprised to see Outlook.com left out of the mix. Personally, I'm still looking forward to having general IMAP support so I can add my self hosted email accounts. The latest version also introduces background syncing for devices running iOS 7, which means your email will already be in your inbox before you even open the app (previously you had to wait for the app to pull down the latest emails after it was opened). Download the latest update for free from the App Store.