We would like to display a list of address. We are trying to design a system where the addresses are only stored in one place, that place being Exchange 2010.
Is there a web service in the Exchange 2010 SDK, that allows us to get the names and address of all users in a group?
Is there a better way to do this, for example getting the data from AD?
I would do this by using the System.DirectoryService.AccountManagement namespace and not through the Exchange Web Services. EWS is more targeted at getting to the information in the Exchange database (email messages, tasks, calendars etc) whereas S.DS.AM is targeted at getting data from Active Directory.
If your domain controllers are running Windows Server 2008 R2 you will have built-in access to web services targetting AD but that's new technology and your company is most likely not using that yet so you'll have to create your own web services wrapping the S.DS.AM-code.
Exchange uses Active Directory to get and update group membership for standard (non-dynamic) Exchange distribution lists so the members of a AD group is the same as the people getting the emails sent to the list. That said, you can use EWS for Expanding Distribution Lists and you might be better off doing this if you're using dynamic distribution groups in Exchange. If you're using dynamic distribution groups in Exchange you need to examine the msExchDynamicDLFilter-value on the dynamic distribution group entry in Active Directory.