Office 365 - Exchange 2010 Hybrid configuration mail flow issues

riverbank used Ask the Experts™
We have configured the Hybrid connector between our Office 365 location and Exchange 2010 server and this has completed without error.

However if we e-mail an e-mail address that only exists in one location then we get an NDR from the other (e.g. e-mail address exists on a mailbox in Exchange 2010, we try e-mailing this from Office 365 mailbox and get an NDR from Office 365 that the address does not exist).

If we set a domain to only exist in one location (e.g. the domain only exists in Exchange 2010) and configure this domain if Office 365 to be the 'Internal Relay' type then mail flow works as expected and this can be delivered.

I believe that we are missing something with the Office 365 portal configuration to allow domains to be configured as the 'shared' type (there is no option for this on the 'accepted domains' tab).

Any suggestions on what we might be missing would be greatly appreciated.
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Configuring the domains as Internal relay is part of the Hybrid process, not sure how you have missed that. In any case, make sure that any domain shared between the on-prem organization and EO has been verified in O365, its domain intent is set to Exchange and the domain type is set to Internal relay (O365 portal -> Admin -> Exchange -> Mail Flow -> Accepted domains -> double-click the domain -> Internal relay).


Thanks for the help Vasil. Your solution mixed with changing the DNS server fixed the issue

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