By default on an on prem Exchange 2013/2016/2019 environment, internal server names are displayed in the message header analyzer, which you would not want to expose externally.

This is how it would look like:

To remove that information, execute this command in the Exchange Powershell. Make sure you have the right Send Connector Name.

Get-SendConnector “Internet” | Remove-ADPermission -User “NT Authority\ANONYMOUS LOGON” -ExtendedRights ms-Exch-Send-Headers-Routing

And now this is how it looks like: