paramailzero.dstreit.com

all changes need to be made to primary, in event they are not, track them and manually re-merge later

if alexandra is logging in to sfreprop.com, it is just alexandra
if alexandra is logging in to dstreit.com, it is just alexandra_dstreit.com

if a primary server goes down, then you change the A record of the mail.dstreit.com to the IP of the secondary you use for failover

Test