Can't reply to old emails after migration even though old legacyExchangeDN is set to migrated mailbox in Exchange Server 2019 and 2016

Applies to: Exchange Server 2019Exchange Server 2016


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-MailboxImportRequest cmdlet.
  • 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.