We have just recently migrated to a hybrid O365 tenant (AD managed on-site). We have several hundred users who work at a company we recently acquired who were brought in with the address user.name@OLDcompany.com. We now need to add an address of user.name@NEWcompany.com and make that the default reply-to address for their outgoing mail. However, we want them to be able to continue to login as user.name@OLDcompany.com and continue to have email sent to that address keep working.
I'm assuming that we'll need to use the Set-ADUser Powershell cmdlet to do this but I'm not sure exactly what I need to add/delete/change in their AD account to make this happen. Any advice would be greatly appreciated.
Thanks!