Emails are not leaving my outbox

Emails remain stuck in my outbox and not being sent, it I shut down outlook, I have to restart my computer, otherwise the program will not start back up again.  when I try to send an email from my windows 8 phone, it tells me there is a specific message stuck in my outbox that needs to be deleted, but when I open the outbox folder, there is nothing in it for me to delete. I have the email address and a screen shot of the error message if someone can check if something on the mail server needs to be cleared.