You might not want to use mail on the server unless your provider has explicitly configured it to do the right thing. It is very easy to get mail wrong, which is why Discourse recommends external mail services.
And with the 3.10.x line of kernels are at least three years old now, that’s not exactly a bleeding edge requirement. Similarly Docker 1.8 is from August 2015. For internet facing servers, you probably should be upgrading distros every two to three years anyway to limit exposure to security significant bugs. (And upgrading components more often.)