I am trying to figure out the scenario. The existing scenario is the as above picture where it is an insurance company consisting of 500 users where both general insurance and life insurance are together. For example. The users UPN is email@example.com and his email is firstname.lastname@example.org .
There is a an order to split the users of general insurance and life insurance to 2 separate domain completely isolated but they would like to maintain the same email address. The objective is as picture below
About 250 users will be moved to a new domain but they'll still be using the existing email address and connected to exchange which is on another domain. May I know what is the best way and can refer me to some link. Thank You