Do you have more than one personal email account or more than one email program with a pile of saved and/or unread mail in it? Think about each of them.
What if it suddenly went away?
Would you be sad or would you shrug?
If the former, find a way to make a backup of the contents. If the latter, decide why you still have it or get rid of it.
(Inspired by the sudden discovery that, not having logged into it in 4 months, my Yahoo Mail account was completely deleted. Presumably they tried to notify me, um, through my Yahoo mail account. First reaction: "Aaaah!" This was followed a moment later by: "Oh. Now I'll never have to sort out those last 50 messages or so that were in there. *shrug*")