Hybrid mail Flow with third party email server

adam900331 366 Reputation points


I have an on-premise Linux server and M365 tenant. I will migrate users from on-premise to Exchange Online. The MX is still pointing to on-premise email system. If the recipient is migrated to Exchange Online, the on-premise relay the email to the cloud. So If something send an e-mail to Exchange Online user through the on-premise e-mail server, the sender mail server will be the on-premise e-mail server. When the Exchange Online Protection receive this e-mail, it will check it the sender domain SPF, in this case the gmail.com SPF. The Exchange Online Protection will see, that the e-mail originating IP is not the gmail public IP, it will see that the originating IP the on-premise e-mail server public IP.

Will it detect the Exchange Online Protection these email as spam? How could it work correctly?


Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
7,487 questions
Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
1,992 questions
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