Exchange Hybrid Deployment single forest multiple email domains

Abdul Farooque 

Fantastic, well done!! 

PeterRising ,,

Yay!!!! It is configured now. 

Abdul Farooque 

If these particular domains are in Exchange Online only, then I would suggest you don't select them in the HCW, as per step 11 in the following;

https://docs.microsoft.com/en-us/exchange/hybrid-deployment/deploy-hybrid#use-the-exchange-admin-center-and-hybrid-configuration-wizard-to-create-a-hybrid-deployment

PeterRising ,

No Peter, this is something HCW team fix this..No such more friendly error. One thing I must mention here that there are couple of domains online (Accepted > MX>Online as well). These domains are not in On-premises Exchnage in Accepted list. 

should I add them and try?

Abdul Farooque 

Does the error show which particular error it is not happy with?

PeterRising ,

Yes, in office 365 all as "Internal Relay, and on-premises as Accepted domains.

Abdul Farooque 

OK, are the invalid domains configured in both Exchange On-premises, and Exchange Online?

PeterRising ,

Yes, the invalid smtp domains error comes in the end when it try to configure mail flow.

Abdul Farooque 

So does it still say "Invalid smtp domain name"?  Is that the error you are referring to?