When Outlook and Exchange communicate they use a proprietary (and complex) MS-RPC based messaging protocol (unless you set them up to use IMAP or POP3, losing all the advanced capabilities of both). RPC does not work well across firewalls, that's why now Outlook supports RPC over HTTP. Basically, it tunnels the proprietary RPC communication inside HTTP, to allow for using Outlook outside the firewall without the need of using a VPN to contact the Exchange server. There is now way you can use it with Mercury, it is a standard SMTP/IMAP/POP server, it doesn't "speak" Exchange protocol.
When Outlook and Exchange communicate they use a proprietary (and complex) MS-RPC based messaging protocol (unless you set them up to use IMAP or POP3, losing all the advanced capabilities of both). RPC does not work well across firewalls, that's why now Outlook supports RPC over HTTP. Basically, it tunnels the proprietary RPC communication inside HTTP, to allow for using Outlook outside the firewall without the need of using a VPN to contact the Exchange server. There is now way you can use it with Mercury, it is a standard SMTP/IMAP/POP server, it doesn't "speak" Exchange protocol.