I would like to determine, which mail notifications to receive. For example I don't want to get notifications about updated Finish Dates. I know this isn't configurable through the web frontend but unfortunately I don't know where to start in the Hardcode. 
This is the only thing I found on the internet: https://community.openproject.com/topics/7385. But this is only about the configuration of the mail layout.

Thank you!

For OpenProject 8.3.1:

Administration > System Settings > Email Notifications tab