If you've ever been editing a PowerMail and received a warning message, the most likely cause is that you are using a browser extension, such as Grammarly, which is inserting extra characters into your email's HTML.
This is an example of what you would see in the HTML Editor
To see if the browser extension may be what is causing this message, click the HTML button in the editor
If you see that the HTML side of your message looks like a confusing mess (more than normal), the browser extension has probably been at work.
You can either clean the message yourself or feel free to send a Support Request and we can clean it up for you. To keep this from happening in the future, please disable your browser extension while working on PowerMails.