I am seeing a conflict between MyMail newsletter shortcode form and having quform installed.
Uncaught TypeError: Cannot read property ‘success’ of null form.js:36 (anonymous function) form.js:36 l jquery.js:2 c.fireWith jquery.js:2 T jquery.js:2 r jquery.js:2
When quform is deactivated, MyMail is able to work perfectly.