Update (13 apr 2011): Rollup 3 for Exchange 2010 SP1 contains UDP support. To enable it, apply RU3 and set HKLM\SYSTEM\CurrentControlSet\Services\MSExchangeRPC\ParametersSystem\EnablePushNotifications to 1 (REG_DWORD). More information in support article kb2009942.
New e-mail notifications from Exchange to Outlook, we receive them all the time. Most of us never look at the technique, because in most cases this works so there’s no need. But what if it doesn’t or you are experiencing delays? With Exchange 2010 this situation is more likely to occur than with earlier versions of Exchange, because many people are still using Outlook 2003 or earlier clients. To understand why this happens, you need to understand how these notifications work (or should I say worked).
Note: To improve readability, you should read “Outlook 2003 or earlier versions in online mode” when it reads “Outlook 2003” from here on, unless states otherwise.
When Outlook 2003 connects to Exchange, it tries to register itself to receive notifications. If registration is successful, Outlook 2003 tells Exchange on what port it expects (UDP) packages to arrive, and it by default this is in the port range 1024-65535. When sending notifications, the Exchange server will also open a dynamic port in this range and connect to the registered client port. After receiving the notification, Outlook 2003 will retrieve the message, will display it in the appropriate folder, make a sound, show a systray icon, change your cursor, etc. When the registration for new mail notifications fails, Outlook 2003 will use a polling mechanism the check for changes.
The related knowledge base article (kb2009942) mentions two solutions. One solution is a mere pretext and explains increasing the polling frequency. To do so, it requires applying Exchange 2010 Rollup 1 on the CAS server and configuring the following registry key on that CAS server:
HKLM\CurrentControlSet\Services\MSExchangeRPC\ParametersSystem\Maximum Polling Freqeuency (DWORD, range 5000-120000)
The reason for performing this step on the CAS server is that Exchange 2010 will determine the polling frequency, not the client. The setting will work immediately, but clients need to reconnect in order for the new value to become effective. Note that setting this value lower than 5000 has no effect because Outlook 2003’s minimum poll rate is 5000.
Another solution is to enable cached mode for Outlook 2003 clients. This will not solve the delay in receiving new e-mail notifications, but it will solve the most annoying issue, being the delay in visual feedback. In cached mode users won’t notice the delay because they’re working with a local copy of their mailbox. Any changes (sends, deletes, moves) will happen in the local cached file (OST), and Outlook will update their Exchange mailbox in the background.
The article fails to mention the third solution: upgrade! The reason Outlook 2007 doesn’t have this issue is that Outlook 2007 (and later) support a third method: asynchronous (push notification). And as you’ve probably guessed, Exchange 2010 (and Exchange 2007) supports this method as well.