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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