1. Prevent inbound/outbound traffic by EndFFX and sending no emails to gateway
2. Stop the gateway service
3. Move the FastFax mailbox to another storage group, perform operations
4. Move the FastFax mailbox back to original location
5. Start the gateway service and start FFX
If you are moving to a new storage group on a permanent basis you will have to uninstall and then once storage group is created do an install.