I have a possibly very stupid question

I just saw, that there is another PM to freyasmom still sitting in my outbox.
I wrote it on the 2nd december. What am I doing wrong?

Hi,

I just wrote a private message a few minutes ago and it is still sitting in the sent box.
Is this because the other user isn't online right now or do I have to do something else in the outbox.
I can't find anything except deleting the pm.