External emails working for other users and not working for some in O365

Immanuel Kituku 0 Reputation points
2024-01-17T01:52:00.3866667+00:00

I am a new employee at my company. We have a hybrid setup for mails whereby we have exchange server 2016 and exchange online. We recently bought a new email gateway. There is an Mx record on our domain registrar that points to the email gateway and all external mail passes through the email gateway first, routed to our on prem server then finally to o365 users for those who are in o365. I disabled Exchange online protection because on the domain page in Microsoft 365 admin center, it was complaining about the Mx record saying it's expecting the o365 Mx record but it doesn't apply to our case. Some users on o365 are getting external mails but others are not getting. I set up a connector on o365 for the email gateway. I have also checked the email gateway to see if the messages were quarantined but they show they have been delivered. When I ran the Get-MessageLogs on exchange on premise, I see the messages are present but on o365 there is nothing when I perform a message trace. I am only seeing internal emails.What could be the issue?

Microsoft 365
Microsoft 365
Formerly Office 365, is a line of subscription services offered by Microsoft which adds to and includes the Microsoft Office product line.
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Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
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  1. Jarvis Sun-MSFT 10,221 Reputation points Microsoft Vendor
    2024-01-17T09:02:02.3333333+00:00

    Hi @Immanuel Kituku , Welcome to our Q&A forum! It seems you’re dealing with a hybrid mail flow issue between your on-premises Exchange Server and Exchange Online. We can try to troubleshoot this step by step:

    1.MX Record Configuration: You’ve correctly set up an MX record pointing to your new email gateway. This is the first step in the mail flow. Ensure that the email gateway is configured properly to route external emails to your on-premises Exchange server.

    2.Exchange Online Protection (EOP):

    You mentioned disabling EOP due to the complaint about the MX record. While this is understandable, EOP plays a crucial role in handling external emails for Exchange Online. Consider re-enabling EOP and configuring it to work alongside your email gateway. You can customize EOP settings to accommodate your specific setup.

    3.Accepted Domains Configuration: In your hybrid deployment, where cloud-based users in Microsoft 365 and on-premises users share the same email namespace, ensure that the domain is set up correctly. Set the domain type to Internal relay. Reference: https://learn.microsoft.com/en-us/exchange/troubleshoot/email-delivery/on-premises-users-not-getting-emails-from-microsoft-365

    Hope the above can help!


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