Has This eMail Been Sent? Help Please! Will Choose Best Answer!?

When I send an email from Craigslist my computer automatically opens up a Microsoft program. I sent a email today and there was an error so I found the email in my drafts and sent it again. It says there is one email in my outbox. When I click on it the message comes up. But up at the top it says "This message has not been sent". When I X out of the Microsoft program it says something like "There are still messages in your outbox. Do you want to continue?" So has the message been sent? Thanks!