Issue with Receiving Emails from External Organisations using Exchange Servers On-Premise

Dear Microsoft Community,

We are currently encountering a critical issue where emails sent from external company using Exchange server On-Premise setup are not reaching our Exchange Online environment. Despite departing from the SMTP of the external partner organization, these emails fail to enter the mail flow within Exchange Online.

It's crucial to note that we have a custom domain configured, and according to the Service Health Report, all settings are in order. However, we must acknowledge that DKIM settings are

currently missing.

Despite our efforts, this specific configuration impedes email traffic flow, significantly impacting our ability to communicate effectively with external partners. Even our external partners and officially configured administrators are unable to resolve the issue.

We urgently seek your insights or assistance in resolving this matter promptly. Your expertise and support are greatly appreciated.

Thank you for your attention

Thomas