Two companies are merging together. Both existing companies have one internal AD domain/forest and one Exchange 2010 organisation.
I have created a new AD single domain, single forest (2016) and Exchange (2016) environment for this new company which is authoritative for the new external email domain, and have a two-way trust between all three. I also have a Exchange Federation Trust and Organisation sharing setup - free/busy information is working. Eventually all accounts from the two old domains/forests will be migrated into the new domain, when this happens the old AD domains will be retired.
The new company has a new external email domain name. From day one all users must have an email address on the new domain name. However, we don’t want to migrate the users into the new AD domain at this stage due to workstation builds, access to resources, old apps etc.
I have been led to believe that I need to make the new Exchange environment authoritative for all three email domain names. Then there is something in Exchange to do with send/receive connectors will is intelligent enough to forward incoming emails to the correct old Exchange environments, in the old domains – therefore landing in the users old mailboxes. I have been told I do not need to create any mailboxes or AD accounts in the new domain for this to work.
User1@newcompany.co.uk gets forwarded to a mailbox in old domain1 i.e. firstname.lastname@example.org
User2@newcompany.co.uk gets forwarded to a mailbox in old domain 2 i.e. email@example.com
Can anyone please help?