On-premises users can't get email messages from Microsoft 365 users in an Exchange hybrid deployment

Original KB number:   2730609

Symptoms

You have a Microsoft Exchange hybrid deployment in which cloud-based users in Microsoft 365 and on-premises users have the same email namespace (such as alias@contoso.com). However, on-premises users aren't getting email messages from Microsoft 365 users.

Additionally, when a Microsoft 365 user sends an email message to an on-premises user, the Microsoft 365 user receives a nondelivery report (NDR) error message that resembles the following:

#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

Resolution

This occurs if the domain that's set up in the hybrid deployment isn't set as a shared domain in Microsoft 365. To fix this issue, set up the domain as a shared domain. To do this, follow these steps:

  1. Sign in to the Microsoft 365 portal as a global admin.
  2. Select Admin, and then select Exchange to open the Exchange admin center.
  3. In the left navigation pane of the Exchange admin center, select mail flow, and then select accepted domains.
  4. Double-click the domain that's set up for the hybrid deployment.
  5. Select Shared, and then select save.

More information

The Exchange admin center lists the domains that you added to your account through the Microsoft 365 portal. It lets you manage how messages are delivered. In a hybrid scenario, Exchange Online must be set up correctly so that when a cloud-based user sends an email message to an on-premises user, Exchange Online routes the email message to the on-premises messaging environment.

For more information about accepted domains, see Accepted domains in Exchange Server

For more information about hybrid deployment, see Exchange Server Deployment Assistant

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