We have a situation in an established rule where occasionally the E-Mail task shows completion, yet the mail message is not sent.  The question is, does workflow wait for a "message sent" message, or does it just want for the mail server to say "I have your request and will take care of it?"

In the first case, workflow would know the message was not sent. In the second case it would not.

I am thinking it's like DCC - WF makes the request and then forgets about it.