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Push e-mail is used to describe e-mail systems that provide an "always-on" capability, in which new e-mail is instantly and 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 e-mail client. Most of today's clients are smartphones.

Contents 1 Comparison with traditional e-mail 2 Mobile users 2.1 BlackBerry 2.2 Windows Mobile 2.3 Other mobile users 3 Simulation using traditional e-mail 4 Protocols 5 Products 6 See also 7 References

Traditional e-mail access over dial-up connections was and still is "pull" based: at login and later in intervals, the Mail User Agent (e-mail reader) polls the Mail Delivery Agent (server) to see if there is new mail, and if so downloads it to a mailbox in the user's home directory. However, mail has always been pushed from the origin to the final Mail Delivery Agent. Extending this push to the last delivery step is what distinguishes push e-mail from traditional e-mail systems.

The reason that pull is the usual method for the last stage of mail delivery is that, while the server Mail Delivery Agent would normally be permanently connected to the network, it does not necessarily know how to locate the client Mail User Agent, which is likely to not only be connected only occasionally, but also to change network address quite often. For example, a user with a laptop on a WiFi connection may be assigned different addresses from the network DHCP server every once in a while and have no persistent network name, and when new mail arrives to the mail server, it does not know what address the client is currently assigned.

Post Office Protocol (POP3) is a popular example of a pull based mail delivery protocol.

The Internet Message Access Protocol (IMAP) provides both polling support and the ability to monitor for notifications – this means that a client can be made aware almost instantly of the existence of the new message, but explicitly fetches new message data. This makes retrieval of the message marginally slower by a matter of a round-trip time, but this is typically only a fraction of a second. Efficiency can exceed a purely-push system because the client can choose to download full messages only as the user requests them.

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Although push e-mail 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 of Asia was the BlackBerry service from Research In Motion. In Japan, "push email" has been standard in cell phones since the year 2000.

BlackBerry uses wireless Mail User Agent devices and a BlackBerry Enterprise Server (BES) attached to a traditional e-mail system. The BES monitors the e-mail server, and when it sees new e-mail for a BlackBerry user, it retrieves (pulls) a copy and then pushes it to the BlackBerry handheld device over the wireless network.

BlackBerry became very popular, in part because it offers remote users "instant" e-mail experience; new e-mails appear on the device as soon as they arrive, without the need for any user intervention. The handheld becomes a mobile, dynamically updating, copy of the user's mailbox. As a result of the success of BlackBerry, other manufacturers have developed push e-mail systems for other handheld devices, such as Symbian based mobile phones.

Microsoft began offering a simulated push experience with Windows Mobile 5.0, and true push technology in 2007 with the release of Windows Mobile 6 under the name "Direct Push Technology". 'Direct Push' technology is an additional feature added to Microsoft Exchange 2003 with a new service pack that adds messaging and security features currently also known as AKU2. CommuniGate Pro has even had PUSH technology built into their Collaboration Suite since 2001 using the IMAP IDLE Protocol. Exchange Server enabled to push Outlook messaging directly to a phone device running Windows Mobile 5, using a subscriber's existing wireless phone account (instead of the device having to "pull" email from the server).

Sony Ericsson Smartphones (M600,P990,W950,P1,w960) feature push e-mail using IMAP IDLE or with the built-in ActiveSync client. Most other Sony Ericsson phones support IMAP IDLE push email quite well (only the inbox however).

Other open push email solutions available in the market today are SEVEN, Visto, and Good Technology (part of Motorola).

The key benefit of Visto Solution is that it works on any SmartPhone Treo680, 700w, and the new MotoQ. SEVEN supports more than 200 devices, covering devices using Symbian, Palm, Microsoft Mobile, BREW and Java/J2ME.

Good Technology's Good Mobile Messaging (formerly known as GoodLink) supports Microsoft Exchange 2000, 2003 and 2007 as well as Lotus Notes.

Visto support Exchange 5.5/2000/2003, Domino all version and works with any ISP email.

SEVEN supports all Exchange and Domino version plus POP and IMAP.

Another company to offer a push email solution is Critical Path, Inc. under the brand name Memova Mobile, the only requirement of this is that the handset have GPRS and MMS capability.

Most of these non-proprietary solutions are network independent, meaning that as long as a device is GPRS enabled and has an email client, it will have the ability to send/receive emails in any country and via any telco that has GPRS on its network. It also means that so long as the device itself is not SIM locked, the constraints of BlackBerry such as Network locking, vendor locking (BlackBerry devices and BlackBerry Connect devices) and GPRS-roaming charges (for non-home access) are not an issue. Pop in a local SIM card in any country the user is in, have the correct APN settings and get your mail at LOCAL rates.

Traditional mobile mail clients may poll for new mail at frequent intervals, without downloading the mail to the client, thus providing a similar user experience as push e-mail.

IMAP in fact allows many notifications to be sent at any time, but not message data. The IDLE command is often used to signal the ability of a client to process notifications sent outside of a command running, which effectively provides a user experience identical to push.

In contrast to traditional e-mail, most of the protocols used in popular current systems are proprietary; for example, BlackBerry uses its own private protocols developed by RIM. Both the Push-IMAP standard and parts of the SyncML standards are attempting to develop more open solutions.

The Lemonade Profile is an IETF modification to IMAP and SMTP to make them more suited to the demands of mobile e-mail, it relies on the existing IDLE (RFC 2177) command to provide instant e-mail notification on the client device. IDLE is not strictly push e-mail although it does provide the same user experience.

• Mozilla Thunderbird^[1] Popular open-source e-mail client for any platform
• BlackBerry The most popular push e-mail solution
• Funambol A popular open-source push-email solution
• Z-push Native opensource ActiveSync implementation
• iAnywhere OneBridge
• iPhone
• Sun Java System Messaging Server from version 6.3
• Microsoft Exchange Server 2003 SP2 and higher
• ChatterEmail for Palm OS
• Critical Path, Inc.
• Dartmouth College Blitzmail
• Kerio MailServer
• Goodlink
• Sony Ericsson
• Visto
• Windows Mobile 6 and higher
• Windows Mobile 5.0 with the MSFP update (AKU2) and higher
• BlueWhaleSystems
• Nokia 770+Nokia N800

• ActiveSync
• Eric S. Raymond's The Cathedral and the Bazaar includes a discussion of the Fetchmail program that is helpful in clarifying the difference between push and pull.