we are in the process of having HA due to combination of issues . One is in case of all the mail box lost due to external attack , human error or software issue . I am not too sure we can recover the data from the other server due to the other server also get the update immediately that changes . I hope other type of risk will work with the HA . our exchange and AD on the hosted solution and hardware level protection with the VM ware .
please share the exchange available option to make the mail availability 24 X 7