As far as I know, there's no way except to look at the header, at the beginning of the post. And that gets truncated if it's too long.
I would be nice if the FR software supported group aliases, so that I could define, for instance, mypinglist to represent some list of names, which would then be expanded automatically when I posted something to that alias.
While I'm at it, it would also be nice if one could FReepmail to more than one person at a time. (As a bonus, this could include oneself; that would provide a mechanism for saving copies of mail that you sent out yourself.)