Does anybody know if it is possible to extract the client operating system of Outlook Anywhere Users? I know that it is possible to get the Outlook Version, but the OS Version would be necessary too. The reason why is that I would like to identify all XP Clients.

Hi,
 
According to your description, I understand that you want to know the system version which is used for Outlook Anywhere connect to your Exchange server.
If I misunderstand your concern, please do not hesitate to let me know.

As far as I know, we cannot get the system information when Outlook client connect to Exchange server. However, we can review the Outlook version by relevant log, for example IIS log, RPC log.
More details about get Outlook client version, for your reference:
https://social.technet.microsoft.com/Forums/en-us/83f20ab0-ddcb-40f0-8a8a-abf8d82b082d/exchange-2007-get-all-client-versions?forum=exchangesvradminlegacy
https://social.technet.microsoft.com/Forums/zh-CN/9ae24612-9b8a-4a21-b676-905930faa4e7/client-version-connections-to-exchange-2010-cas?forum=exchange2010

Best Regards,
Allen Wang

While a great way to get this information is to search the Exchange logs and see if you can find it, you may end up missing some computers in your environment running Windows XP since they will not be using Outlook Anywhere.  A better way to get a list of clients running Windows XP might be to query Active Directory for that information. Take a look at article below that describes how to do this:

http://blogs.technet.com/b/ashleymcglone/archive/2014/01/30/use-powershell-to-find-windows-xp-computers-still-alive-in-your-active-directory-domain.aspx

Our problem is that not all computers are Active Directory members.

Hi 

Exchange Server can show you the client logon statistics you can where view users currently connected to exchange server, client ips, time last accessed.