For a custom non-delivery report (also known as an NDR or bounce message) in Microsoft Exchange Server 2019 or Exchange Server 2016, the foreign language characters set in the RejectMessageReasonText parameter of a transport rule aren't displayed correctly.
To fix this issue, install one of the following updates:
For Exchange Server 2019, install the Cumulative Update 6 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.
For Exchange Server 2016, install the Cumulative Update 17 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
Learn about the terminology that Microsoft uses to describe software updates.