Thank you very much for this thread, which gave me sufficient hints to discover yet another solution (as I wasn't able to install .NET 3.5 framework):
https://support.microsoft.com/en-us/help/3186435/sql-server-2016-database-mail-doesn-t-work-when-net-framework-3-5
Their workaround #1...
- This reply was modified 5 years ago by mkirschner. Reason: Correction