At first blush it looks like a potential great market; however, think of the potential for unintended information to get passed to the new owner. If someone was using
[email protected] then the new owner would likely get lots emails that were intented for the previous owner, at least at first.
These emails could potentially have passwords on them and/or lots of other stuff. It seems that there would be too much risk to sell it in most cases. Somewhere you would think there would be value, but it probably lies in the first owner using the email as some sort of development and/or marketing plan.