We deploy hybrid exchange using the HCW, AADC has been deployed as well. Mailbox A is created on exchange online. Mailbox B is created on exchange on-prem.
Now I can send an email from A to B. But I cannot send an email from B to A. It says "We won't be able to deliver this message to A because the email address is no longer valid"
A friend told me, it is because A is created on the Exchange online, so B cannot find it. Or the other hand, B is created on on-prem and have is synchronized to the cloud by AADC, so A knows it and can send email to it.
Is it true? In my opinion, once a hybrid exchange environment has been deployed, the exchange online and exchange on-prem should be able to talk with each other. So there should not be an issue when you send email across online and on-prem.
If my friend is true, what should i do the synchronized the mailbox from online to on-prem?
If my friend is wrong, which part of the setting could be wrong?