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: