My sent emails on MAIL go to the outbox :(

When I try to send an email on MAIL, it goes to the outbox instead of being sent, and stays there 😟. I have tried many things without luck:

I have closed mail, opened Safari, returned to Mail and sometimes this action gets it to be sent, but not often. I have restarted the computer.

I have shut down the computer and opened it later, but 99% of the time the email is still stuck in the Ourbox. I have called Cox and verified

that my computer is able to send emails from the Cox web page. I receive those emails, but they do not show up in my SENT folder. Even

when my emails are sent, they do not show up in my SENT FOLDER. Very very frustrating. The Cox person with whom I spoke told me they

have been receiving many complaints about the same problem, emails getting stuck in the Outbox instead of being sent, and they believe

that perhaps Cox has made some change with MAIL which is not compatible with Cox ? I have Maverick on OSX 10.9.5. CAN ANYONE

PLEASE TELL ME WHAT TO DO SO MY SENT EMAILS WILL "GO" NORMALLY AGAIN? Thanks