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Push email is an email system that provides an always-on capability, in which new email is actively transferred (pushed) as it arrives by the mail delivery agent (MDA) (commonly called mail server) to the mail user agent (MUA), also called the email client.Email clients include smartphones and, less strictly, IMAP personal computer mail applications.When "Push" is configured, emails arriving into the Microsoft Exchange inbox are instantly pushed to the device.Calendar events sync both ways between Exchange and the device.In Japan, "push email" has been standard in cell phones since 2000.Apple's i Phone, i Pad and i Pod Touch support Hotmail push email.
Microsoft began offering real-time email notification with Windows Mobile 2003 (sending SMS messages when new mail arrived), then replaced it with a simulated push experience (long polling) in 2007 with the release of Windows Mobile 5 AKU2 under the name "Direct Push Technology".
This makes retrieval of new messages more flexible than a purely push system, because the client can choose whether to download new message data.
Although push email had existed in wired-based systems for many years, one of the first uses of the system with a portable, "always on" wireless device outside Asia was the Black Berry service from Research In Motion.
Android's built-in Gmail client uses Google Cloud Messaging to push email for Gmail accounts set up to sync with the phone.
Android also supports Microsoft Exchange accounts natively through its default mail application.