In a Microsoft Exchange Server 2019 or 2016 environment, consider the following scenario:

  • You assign the Mailbox Import Export role to administrators by using the following cmdlet in Exchange Management Shell:

New-ManagementRoleAssignment -User administrator -Role "Mailbox Import Export"

  • You create mailboxes as migrated users, for example, User A and User B. (Assume that User A is User 1 and User B is User 2 in the old Exchange organization.)

  • You add the legacyExchangeDN attribute of the old Exchange organization as X.500 address to User A and User B by using the following cmdlet in Exchange Management Shell:

Set-Mailbox -Identity -EmailAddresses

  • You import the PST files into the migrated users’ mailboxes by using the New-MailboxImportRequestcmdlet.

  • You sign in to Outlook on the web (formerly known as OWA) as User A.

In this situation, you see email messages from User 2 to User 1 in Inbox. However, when you reply the email messages, you will receive an NDR message.


To fix this issue, install one of the following updates:

For Exchange Server 2019, install the Cumulative Update 2 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.

For Exchange Server 2016, install the Cumulative Update 13 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.


Learn about the  terminology that Microsoft uses to describe software updates.

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