I have two Active Directory Domains (C1.com and C2.com) in separate cities that are not in the same forest. C1.com and C2.com are syncing to separate Azure subscriptions with Azure AD Connect. I use the C2.com domain for user authentication in this Azure subscription and for website addresses.
I have a single Exchange server in C1.com that accepts email messages for C2.com as an alias for users. (me@C1.com has a secondary email address from me@C2.com). There are also some email-only (non-AD) domains that are used as aliases. This works well and has been for many years.
Now I want to migrate my Exchange server to Office 365 E3. I signed in to the Office365 portal and added my account to my account without any problem using the TXT record. I also just added the email domains. I have not changed the MX records yet.
When I add the C2.com domain, I receive the message "We have confirmed that you own C2.com, but we are unable to add it to this client at this time." The domain has already been added to another Office 365 tenant: UserC2onmicrosoft .com. "
All I need is the ability to forward emails from C2.com to Office365. I'm not really interested in the AD users in Office365. I've seen this article https://docs.microsoft.com/en-us/azure/billing/billing-subscription-transfer, but I'm not sure he'll do what I want. Since both domains in Azure are running a client production workload, I need to understand the implications of every change I make before I start reconfiguring things.
Thank you in advance for any help and advice.