When you are trying to send messages and they stay in the outbox you can try to do the following to correct the issue

1. Move all messages to the drafts folder or delete the ones that are not needed
2. Once the outbox is cleared do a send/receive of email to make sure there are no errors
3. Go to the draft folder and attemtp the send the messages again one at a time. Do not try to resend all send one wait till it leaves and send another one.?
4. If you have a message that will not send but others do then there is something wrong with that particular email. Delete it and start over
5. If no messages will go then there is something wrong with the mail program on your computer and will require a computer technician.?