Regardless of whether the receiver uses polling e-mail, outgoing mail is generally pushed from the sender to the final mail delivery agent (and possibly via intermediate mail servers) using Simple Mail Transfer Protocol. However, if the receiver uses a polling email delivery protocol, the final step from the last mail delivery agent to the client is done using a poll. 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. Extending the "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.
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.[citation needed]
Apple's iPhone and iPod Touch support Yahoo! push e-mail, Hotmail push e-mail (activated through the Dinsdale Panel), 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 Connect. Apple's own MobileMe subscription-service for push email, contacts, and calendars is also supported.
BlacMail, from Fifth C, is a push e-mail solution that supports all major public email systems and targeted at mass-market consumer phones. The solution is unique in that a single client supports both SMS or GPRS as the message bearer, important attributes in the fastest developing mobile markets such as India.
Android's built-in Gmail client uses Google Sync to push e-mail for Gmail accounts set up to sync with the phone.
Android also supports Microsoft Exchange accounts natively through its default mail application. Emails arriving into the Microsoft Exchange inbox are instantly pushed to the device. Calendar events sync both ways between exchange and the device. Yahoo email is not pushed to an android device. An alternate to lack of native support for yahoo mail is to install the free yahoo mail app which provides instant push email. Recently also Hotmail has been made push configurable for Android smartphones through the default mail application.
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.
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.[citation needed]
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Android's built-in Gmail client uses Google Sync to push e-mail for Gmail accounts set up to sync with the phone.
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