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O365 Hybrid email flow

I am in a hybrid environment running O365 and on premise 2016 exchange. All emails have to flow through on premise Exchange. we are using the filtering and compliance solutions that are already on-premise.

The question I have is this, assume that the on premise exchange is down. Now a staff logs into O365 portal and composes an email to another staff (also in O365). Would the email be delivered?
3 Solutions
AmitIT ArchitectCommented:
No, it won't be delivered. Mails will be queued up. Until you bring back on-premises server back up.
timgreen7077Exchange EngineerCommented:
No the emails will not be delivered. You will need to disable that send connector in O365 and allow the mail to go out O365 instead of your on-prem environment. Once the on-prem server is back up and running, just re-enable the connector in O365 and it will start sending mail on-prem again.
Vidit BhardwajAdminCommented:
That's correct emails will not be delivered if you have centralized mail flow enabled in hybrid config
Aaron GuilmetteTechnology Solutions ProfessionalCommented:
No. If you have enabled Central Mail Transport, then Mail will not be delivered if on-premises Exchange is unreachable.  CMT processes all Mail, including messages sent between cloud mailboxes.
timgreen7077Exchange EngineerCommented:
question has been answered. closing ticket and assigning points.
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