Separate Users from existing domain but still maintain same exchange server

[nivenpeter]

Hi Experts,

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 john@covid19.local  and his email is john@covid19.com . 

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

Surnder Peter

[#2]

Hello,
I deployed and administered in the past an Exchange Server in a resource forest scenario, looks like you would need to do that here, this also involves making a trust relationship between the domains (old and new) and creating mailboxes for the new domain users in the current Exchange Server.

Some reading so you can continue https://docs.microsoft.com/en-us/exchange/deploy-exchange-2013-in-an-exchange-resource-forest-topolo...