Answer
Yes. The GMS Outlook MAPI Connector and GMS Instant Messenger can be used with Proxy servers.
GMS Webmail: If HTTPS is being used through a Proxy Server then proxying for connections on Port 8377 needs to be enabled.
GMS Instant Messenger: The windows client version of GMS Instant Messenger will need to be used to access via a secure port.
Keywords:Outlook MAPI Connector Proxy Server HTTP HTTPS SSL IM