How to configure Outlook Anywhere by GPO?
1. Download the Article-961112.adm package from Microsoft site.
2. In the Group Policy Object Editor add the Article-961112.adm file. Click right Administrative Templates and Click Add/Remove Templates. Click ADD, locate and select Article-961112.adm file and click Open.

3. Under User Configuration -> Policies -> Administrative Templates -> Classic Administrative Templates -> Article 96112 Policy Setting -> Outlook Anywhere (RPC/HTTP) configure details:

a) RPC/HTTP Connection Flags â?? Flags: 1 + 2 + 3 +6(Flag1: Enables the ‘Connect to Microsoft Exchange using HTTP checkbox’ on the Connection tab, Flag2: Enables the ‘Connect using SSL only’ checkbox, Flag3: Enables the ‘Only connect to proxy servers that have this principal name in their certificate’ checkbox, Flag6: Enables the ‘On slow networks, connect using HTTP first, then connect using TCP/IP’ checkbox),

b) Proxy Server Name â?? mail.contoso.com,

c) Only Connect if Proxy Server certificate has this principal name â?? msstd:*.contoso.com

d) Proxy authentication Setting â?? NTLM.

4. Save GPO.
5. Take a look on client Outlook configuration.