My Mackbook Pro Mail application is whizzing out?

Earlier today I attempted to send an email on the mail application on my MacBook Pro. I didn't realize that it had said the login failed until after I attempted to send the email, now every time I click on the mail application, the email I tried to send earlier pops up like every 2 seconds and goes away instantly, it continues to do this over and over and over until I finally just quit the application. I have no clue how to fix this and need help ASAP! Thanks!