Messaging gateway HA active/passive mode

Hi all,

I would like to know that if SMG be configured in HA mode active/passive mode, I know that HA option is not built in to SMG, but if i confgure another SMG virtual appliance and provide it with different public IP address from seperate provider,  My client  wants to have HA for SMG in active/passive mode. So the plan is i would prepare another Virtual machine with exact settings as the primary one, then modify the DNS MX record providing lower preference to the second machine. If the primary goes down, secondary VM will be selected on the basis of DNS records.

Just need to know that if this scenrio would work?

Thanks and your help will be much appreciated.