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