how do i delete an email that wont send but keeps trying repeatedly?

I have an email i tried to send using my gmail account and it keeps giving me the error that it is too large of an attachment to send. Yet every time i open the eM Client it tries to resend it and gives me another error. When i close the eM Client it gives me an error that there is still a message trying to be sent. How do i get a rid of this problem?

have you tried to delete this message from your “Outbox” folder?