• Insights

Mailbox Sync Delays with Outlook 2003 and Exchange 2010

Joseph Hoegler

3 min read

All Insights

At a few recent client implementations, we have seen noticeable delays synchronizing various changes in mailboxes to Exchange 2010 when running Outlook 2003 in Online Mode.  As it turns out, this is a known issue and Microsoft has documented it at http://support.microsoft.com/kb/2009942.  The following are symptoms of the issue:

    • Outgoing messages stay in the Outbox for up to 1 minute


    • New messages do not arrive in the mailbox for up to 1 minute


    • Items that are deleted or moved between folders may take up to 1 minute for the change to be reflected

This issue does not happen with Outlook 2003 in Cached Mode or in Outlook 2007/2010 in Online or Cached Mode.  The issue arises because Outlook 2003 requests UDP notifications from Exchange to determine when to retrieve messages.  When a new message arrives in an Exchange mailbox, Exchange 2007 and earlier would send a UDP notification to Outlook, which would then trigger Outlook to retrieve the message and display to the user.  In the absence of receiving any UDP notifications from Exchange, Outlook reverts to a scheduled polling of Exchange that occurs every 60 seconds, by default.

Exchange 2010 no longer issues UDP notifications to Outlook and, as a result, Outlook is then wholly dependent on its own polling frequency to retrieve new messages.  Outlook 2003 in Cached Mode and Outlook 2007/2010 are not affected by this issue because the former uses a different synchronization algorithm to send or retrieve content and Outlook 2007/2010 use an asynchronous notification process that does not rely on UDP notifications.

There are a few solutions and a workaround for the problem, as I note below.

    • Implement Cached Mode for Outlook 2003 – This solution resolves the issue, as described above, but still leaves a legacy Outlook client in use.


    • Upgrade to Outlook 2007/2010– We recommend that firms strongly consider upgrading the Outlook client to 2007/2010 when deploying Exchange 2010 due to all of the new features that require a newer Outlook client (OAB web-based distribution, Autodiscover, Personal Archive, etc.).  We also recommend Outlook in Cached Mode as a best practice, provided workstation hardware is sufficient for mailbox sizes.


    • Reduce Polling Frequency of Outlook to Exchange– This involves the steps as outlined below to add a registry value on the Exchange 2010 CAS role to reduce the maximum polling frequency of Outlook.  While the registry value supports anywhere from 5 seconds to 2 minutes, Outlook 2003 cannot poll any more frequently than every 5 seconds.  As a result, this represents a best case scenario for Outlook 2003 in Online Mode and something where users will still likely notice delays.
        • Install Exchange 2010 Update Rollup 1.


        • On all Exchange 2010 CAS servers, navigate to  HKLMSystemCurrentControlSetServicesMSExchangeRPCParametersSystem and create a REG_DWORD entitled “Maximum Polling Frequency” with a value from 5000 to 120000 (decimal value).
            • Note that, as mentioned above, configuring this to anything less than 5000 will have no additional effect on Outlook 2003.


        • Restart the Microsoft Exchange RPC Client Access service on your CAS servers.  You shouldn’t need to restart your Outlook clients but you may want to as well.

Update:  As of 10/27/10, Microsoft has confirmed that this registry value can be configured as 5000 and result in a 5 second polling frequency.  It was previously documented that anything below 10000 would have no additional effect on Outlook polling.

Update:  This specific issue, related to UDP notifications, was formally resolved in April 2011 via Update Rollup 3 v3 for Exchange 2010 SP1 (see http://support.microsoft.com/kb/2009942 for information and the steps to re-enable UDP notifications).  Unfortunately, there were some additional permutations of this type of problem discovered for all versions of Outlook when operating in Online Mode, not just Outlook 2003.  These have been resolved in Exchange 2010 SP2 (see http://support.microsoft.com/kb/2579172 for more information).