Of course, all this merely raises the problem that
leaked emails are hardly a RS until they get quoted by somebody and are alchemically
transmuted into RSs.
There is no such thing as a "reliable source". The reliability of a
source depends on what it is being used as a source of. The leaked
email, whether direct or quoted, is not a reliable source for anything
contained in it. The article that quotes the email, however, is a
reliable (primary) source for the *claim* that the email was leaked.
All we have to do is prefix the appropriate sentences of our article
with "So-and-so claims that", and the sources qualify as reliable.