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??

thanks!