Mosaico returns 403 error due to data-bind attribute in template html
Wordfence uses knockout.js for data binding. I see Mosaico adds data-bind attribute to the HTML input which is considered prone to XSS attack by knockout and 403 error is shown by wordfence.

I've disabled XSS in the Wordfence setting and the mailing is working correctly for now. Happy to look for answer if there is a way to avoid XSS attack in mosaico template builder?