Thank you Andrea -- that sounds good.
In case of disaster, where the new server goes offline for several days, what would I need to do to make Smartermail work again on the old one? Would it be enough to just turn the service back on and update DNS, or are there specific steps to reactivate the license on the old machine?
My case is just a company mail server, not handling umpteen hosting clients, so half a day of no mail is OK but several days is not. My vision was: if the new server has a disaster (major hardware failure or hacked and must be rebuilt), and will be offline for a period of days, then I can just restart the Smartermail service on the old server, and update DNS records, and have mail going to the old server within a few hours.
I don't use webmail, so access to message stores on either machine is not essential. Just need to be able to send and receive new messages.