@radhakrishnanmu Thanks for your input. The root user has remote access enabled as also the db user I created myself. The issue persisted on a fresh ubuntu 16.04 install created on Digitalocean.
After creating a new server with Ubuntu 14.04 and reinstalling EE it finally worked!
It seems to be something related to the Ubuntu 16.04 + EE. I also followed instructions on this EE tutorial https://easyengine.io/tutorials/mysql/remote-access/ - After all, I'm not not sure if that's what solved the issue, but as long as it works I'm fine with Ubuntu 14.04 + EE.