We are planning to start crossforest migration for our customer. (oldomain.com --> newdomain.com)
For a period of time, users in the organization will be in two different Exchange Servers (some of them will be on Exchange 2013 and some of them will be on Exchange 2016).
Of course, users will need to communicate (send/receive emails, contact list etc.) each other in two different exchange servers for a period of time until we complete migration of the very last user from old domain to new domain.
I read a few articles about coexistence but I couldn't figure it out exactly. Some of them recommending to add temporary smtp address (eg temporary.newdomain.com --> user1@temporary.newdomain.com) to all users which will be migrated and add this domain to SendConnector and ReceiveConnector in old and new servers respectively.
What is the best practice or "suitable way" to provide coexistence for mail flow in two different Exchange servers?
Your valuable comments and guidance will be greatly appreciated.
(References I read: https://www.easy365manager.com/targetaddress/ & https://social.technet.microsoft.com/Forums/office/en-US/0848532c-ac08-4998-869a-94de7502506c/cross-forest-migration-exchange-2013-to-exchange-2016?forum=exchangesvrgeneral)