If you send a user a mail from acp>users>send mail and have wrong smtp settings, you will always get a "mail was sent to ... " reply. The server log contains the correct error message.
In general, this isn't something we've tried to do - the total indicates the number of matches. However, I have tweaked this for 1.3 to tell you if sending failed. (Note that it only tells that if the failure happened immediately.)
