Setting up hybrid exchange online. The is a test environment so we can make any changes for testing. We have Internet > Edge Server > Hybrid Server > CAS/HUB Server > Mailbox Server. We can email from 365 mailboxs account (either cloud only or AD sync object) to on-premise fine and to external domain. But we cant get from On-premise mailbox to 365 mailbox. Says recipient not found. How do On-Premise know or distinguished between 365 mailbox and on-premise? Is there an attributes that need populated in AD?
We are using AD Connect to sync AD to 365. We are on E5 License.