I don't remember ever trying to send it. If I did, I drafted it without a recipient. It's a reply, but only includes the subject from an email sent to me by a department store, includes no text from a previous msg or text that I ever added or an intended recipient. Very odd.
It seems to be some kind of glitch though not a serious one. The only other thing I can think to offer is you rebuild your mailbox (Mailbox, Rebuild) though perhaps not deserving for such a trife. I can't think of anything else.