When you drag an email message from Microsoft Outlook to the desktop in Microsoft Exchange Server 2019 or Exchange Server 2016, the formatting of the file on the desktop is changed. This issue occurs when you use the Outlook desktop app (Outlook for Windows or Outlook for Mac) in Online mode.
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. (See updates below)
For Exchange Server 2016, install the Cumulative Update 17 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016. (See updates below)
Update 1 (Dec 2020): The changes were reverted back in cumulative update (CU) 8 for Exchange Server 2019 and CU19 for Exchange Server 2016 due to a regression. This issue will be fixed again in later CU and the KB article will be updated with relevant details.
Learn about the terminology that Microsoft uses to describe software updates.