We have a office 365 tenant and have a hybrid exchange environment with email addresses as @abc.com .
All our mailboxes are in office 365 and the MX record are pointing to abc-com.mail.protection.outlook.com.
We have another sub-organisation which has email addresses as @def.com.
They have on premises exchange environment and use could based Secure Email Gateway as their MX record.
There is a requirement to setup a new verified domain in office 365 as @abcanddef.com in the @abc.com tenant.
Users from both the domains will have email addresses as @abcanddef.com.
Users from @abc.com domain :-
- They will retain their old @abc.com address and also have new @abcanddef.com address.
- Outbound mail Sender address will be @abcanddef.com address
Users from @def.com domain :-
- Do not need to be consumed in @abc.com tenant in office 365 to avoid license use
- Inbound mail for users in @def.com sent to @abcanddef.com address
- Outbound mail for users in @def.com sent from @abcanddef.com address from their on-premises exchange
What is the best way to set this up?