There is an option to sync Hotmail e-mails (others have too) that says "as items arrive".
How exactly it works? It is something like Hotmail does in Desktop when pinned in IE9 (long pooling) or something else?
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When you setup an Exchange ActiveSync account, the default synchronization mode may be Direct Push. With Direct Push, the device maintains an open connection so that information is delivered to the device as it becomes available. The setting for Direct Push on a Windows Phone 7 device is called, “as items arrive.” The alternative is a Scheduled Push mode where the device is set to check for new messages at a set interval.
What they mean by in open connection is through a unique identifier. This does not drains battery as no data flow is taking place all the time. Only your Data connection is alive as per usual and even when its sleeping or idling, the phone receives info from Hotmail because Hotmail knows where to send this info.
Its like a pipe connected from phone (A) to Hotmail (B) but no water flowing unless there is a need to. When you have a water to flow, B sends out a "trickle" to A to open up and establish contact and the water flows through. All this is through a unique identifier which B uses on the network. In addition the phone (A) also periodically sends out trickles to hotmail (B) after studying network conditions. So direct push adjusts to any network conditions when sending out email.
When configuring e-mail accounts, I've noticed that my Exchange accounts all default to
as items arrive but my other personal accounts (Hotmail, Yahoo & Gmail) are set to have a synchronization time by default. Only the Yahoo account doesn't seem to have the option
as items arrive backing up the theory that the e-mail provider is also responsible for this option to work seamlessly.
It would be difficult to say for sure, as it is a closed source system, but I would imagine it uses the Microsoft Push Notifications service, in the same way that an application can for updating live tiles; in this manner there is no need to poll, which can obviously save bandwidth requirements.