I sent one yesterday not had a reply yet, if you mean you've had an email back saying undelivered then i've not had one of those, or is there another way of checking through my profile.
AFAIK, normal process is that you get a copy of the message you sent to another member directly to your email address as a reference. So if you don't receive one of these then it probably didn't get sent (yet, as there may be server delays for some reason).