Push e-mail is used to describe e-mail systems that provide an always-on capability, in which new e-mail 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 e-mail client. E-mail clients include smartphones and, less strictly, IMAP personal computer mail applications.
Comparison with polling e-mail
Post Office Protocol (POP3) is an example of a polling email delivery protocol. At login and later at intervals, the Mail User Agent (client) polls the Mail Delivery Agent (server) to see if there is new mail, and if so downloads it to a mailbox on the user's computer. However, outgoing mail is generally pushed directly from the sender to the final Mail Delivery Agent. Extending this push to the last delivery step is what distinguishes push e-mail from polling e-mail systems.
The reason that polling is often used for the last stage of mail delivery is that, although 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 may only be connected occasionally and also 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 periodically and have no persistent network name. When new mail arrives to the mail server, it does not know what address the client is currently assigned.
The Internet Message Access Protocol (IMAP) provides support for polling and notifications. When a client receives a notification from a server, the client may choose to fetch the new data from the server. This makes retrieval of new messages more flexible than a purely-push system, because the client can choose whether to download new message data.
Mobile users
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 e-mail" has been standard in cell phones since 2000.
Apple iPhone and iPod touch
Apple's iPhone do not support background services, this means that there is literally no push mail when the phone is in standby mode. To overcome this Apple have integrated the Apple Push Notification Service in the OS3. To use the service each email provider must build a separate notification service and connect it to the Apple Push Notification Service, and as usual have the application approved. When the phone is turned on Apple's iPhone and iPod touch support Yahoo! push e-mail, Gmail push e-mail (via Google Sync) and Microsoft's Exchange ActiveSync platform allowing them to synchronize e-mail, calendars and contacts with a Microsoft Exchange Server, Zimbra, NuevaSync or Kerio MailServer. Apple's own MobileMe subscription-service for push email, contacts, and calendars is also supported.
Google Android
Google's Mobile OS supports Push e-mail based on Microsoft's ActiveSync platform, including push GMail.
Helio Ocean
Helio began adding support to its "ultimate inbox" for push e-mail to the Helio Ocean in July 2007 with support for Yahoo! Mail, Windows Live Hotmail, and AOL Mail. On April 23, 2008 push support was added for Gmail, along with automatic notifications for POP and IMAP services.
Microsoft Windows Mobile
Microsoft began offering real-time e-mail notification with Windows Mobile 2003 (sending SMS mesages when new mail arrive), 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". 'Direct Push' technology is an additional feature added to Microsoft Exchange 2003 with service pack 2 that adds messaging and security features. A phone device running Windows Mobile 5 is enabled to poll Exchange Server each 30 minutes. If new mail arrives in polling interval, it is instantly pulled using a subscriber's existing wireless phone account (this allows device to have changing IP or traverse NAT/Proxy). To achieve push mail with e-mail providers other than Exchange, there is a commercially available plug-in from Emansio that enables push mail with almost any public e-mail provider (such as Google, AOL, GoDaddy), or any e-mail server that supports IMAP-IDLE. Additionally, a free, open-source, executable has been developed to take advantage of the IMAP-IDLE command.
Nokia Symbian Series 60
Some Nokia Symbian S60 models support basic IMAP IDLE functionality with its built-in client.
Mail for Exchange
The Nokia Eseries smartphones and select models of Nseries smartphones support the Mail for Exchange software, which is compatible with Microsoft Exchange Server Active Sync and Direct Push, allowing the Nokia smartphones to receive push email as well as sync contact lists, calendars, and tasks with Exchange servers. Global Address Lookup is also supported, starting with version 2 of the Mail for Exchange software.
Nokia Messaging
Nokia Messaging Email is a push e-mail service and client application, that supports most of the popular e-mail providers like Hotmail, Yahoo! Mail, GMail and many more. Nokia Messaging servers aggregate messages from up to ten accounts on and pushes them to compliant devices (Nokia S60 and some S40, plus Maemo-based devices like the N900).
Palm OS
Palm Smartphone devices such as the Treo have had IMAP IDLE available through the use of 3rd Party software ChatterEmail as early as 2004. There is no additional server software required.
Palm webOS
The Palm Pre webOS has push email for Gmail, IMAP, and Exchange accounts.
Research In Motion BlackBerry
RIM's 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; 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- and Windows Mobile-based mobile phones. However, IMAP synchronization through BlackBerry Internet Service is not two-way.
Sony Ericsson
Sony Ericsson Smartphones (M600, P990, W950, P1, W960, W995, G900, G700) as well as some Cybershot phones (K790, K800, K810, K850, C510, C905) feature push e-mail using IMAP IDLE or with the built-in ActiveSync client (developed by Dataviz). Most other Sony Ericsson phones support IMAP IDLE push e-mail quite well (only the inbox however).
Other mobile users
Other open push e-mail solutions available in the market today are NotifyLink, Visto and Good Technology (part of Motorola) as well as Synchronica.
NotifyLink supports the following backends: Alt-N Technologies, Communigate Pro, Kerio MailServer, Meeting Maker, Microsoft Exchange 2000/03/07, Mirapoint, Novell GroupWise, Oracle, Scalix, Sun Java Communications Suite, and Zimbra, plus other solutions for e-mail only. The supported mobile devices/operating systems include Windows Mobile, BlackBerry, Symbian OS and Palm OS.
The key benefit of Visto Solution is that it works on any SmartPhone Treo680, 700w, and the new MotoQ.
Good Technology's Good Mobile Messaging (formerly known as GoodLink) supports Microsoft Exchange 2000, 2003 and 2007 as well as Lotus Notes.
Visto supports Exchange 5.5/2000/2003, Domino all versions and works with any ISP e-mail. Visto acquired Good at early 2009 and changed their Company name as GOOD.
Synchronica provides a client-less, carrier-grade push Email and synchronization solution based entirely on open industry standards. Their core product, Mobile Gateway, supports push mail standards like IMAP, IDLE and OMA EMN as well as PIM synchronization using OMA DS (SyncML). Towards backends, it supports POP, IMAP, Microsoft Exchange and Sun Communications Suite.
Peek provides mobile push email for consumers. They have their own device, very much like the BlackBerry. Peek supports POP and IMAP, with compatibility to 'Yahoo Mail', 'AOL Mail', 'Hotmail', and 'Gmail'. The Peek device is email only and does not provide voice or any other converged services available on cell phones.
Another company to offer a push e-mail 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 e-mail client, it will have the ability to send/receive e-mails 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.
Simulation using traditional e-mail
Traditional mobile mail clients may poll for new mail at frequent intervals, with or 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.
Protocols
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.
IETF Lemonade is a set of extensions to IMAP and SMTP to make them more suited to the demands of mobile e-mail. Among the extensions are rapid IMAP resynchronization and a new NOTIFY command in IMAP.
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