Almost everyone has hundred thousands of emails laying around. All in your name, all forever stored, all with a legal signature on them binding you, and each with a short text message with no context. It is very often used as evidence, attached with a conjecture provided by the prosecutor. The defended is then forced to try defend themselves both regarding the conjecture, but also having to remember and explain the original context.
It has been used in a profile case to "prove" conspiracy, and has also been used by prosecutors to move public opinion by providing snippets (official sanctioned leaking) to media.
This is why I view running a email server without full disk encryption to be negligence, and that everyone should have their own mail server. Until the legal system have caught up with technology, its not much more one can do.