Default [Q] False Notification of failed sending of email

Howdy kids...

I am getting a "notification" that I have an email that failed to send. When I click on it it takes me to the sending folder of one of my email accounts but its empty. I check all the other accounts and they are empty as well. If I clear the notifications it goes away but will return on phone reboot.

I thought about clearing the mail apps cache but was uncertain as to any issues with doing this.

Any ideas of what to do to get rid of that annoying notification??