When you use delegates in Outlook 2010 or Outlook 2007, it is recommended that the manager and all the delegates use Outlook 2007 Service Pack 2 or higher

When you use delegates in Outlook 2010 or Outlook 2007, we recommend that the manager and all the delegates use Microsoft Office Outlook 2007 Service Pack 2 (SP2) or higher, including Microsoft Outlook 2010. The manager and the delegates are not prevented from running mixed versions of Outlook in an Outlook 2010 or Outlook 2007 SP2 environment. However, we strongly recommend that such an overlapping period with versions earlier than Outlook 2007 SP2 be kept as brief as possible.

In earlier versions of Outlook, such as Outlook 2003 and Outlook 2002, the manager and the delegates can use different versions of Outlook. For example, the delegates can use Outlook 2002, and the manager can use Outlook 2003. However, we do not recommend this configuration.

Although Outlook 2010 and Outlook 2007 do not disable the functionality that lets the manager and the delegates use different versions of Outlook, we recommend that the manager and all delegates use Outlook 2010 or Outlook 2007 SP2 (or later). By doing this, you improve calendar reliability. We recognize that users who cannot upgrade to the same version of Outlook at the same time may have to run mixed versions of Outlook. However, you should limit such a mixed-version topology to a short time during an upgrade period (approximately two months). If you encounter calendar reliability issues, deploy Outlook 2010 or Outlook 2007 SP2 for the manager and for all their delegates as your first troubleshooting step. Then, determine whether the issue continues to occur before you take additional troubleshooting steps.

If either the manager or the delegates use Microsoft Entourage 2004 for Mac version 11.3.0 or a later version, you can have a mixed manager-delegate topology. For more information about the Microsoft Office 2004 for Mac 11.3.0 Update, click the following article number to view the article in the Microsoft Knowledge Base: Note Entourage clients cannot connect with a Microsoft Exchange Server 2007 mailbox for delegate rights assignment unless public folders exist in the Exchange 2007 organization. If public folders do not exist in the Exchange 2007 organization, use one of the following workarounds:

• Add a public folder store to the Exchange server. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
  924625  (http://support.microsoft.com/kb/924625/ ) When you use Outlook with an Exchange 2007 mailbox, you cannot connect to Exchange 2007, and you receive an error message
• Move both the delegate and the manager to Outlook 2010 or Outlook 2007 SP2 (or later). Neither Outlook 2010 nor Outlook 2007 require public folders in order to access an Exchange 2007 or later mailbox.