Mail Delivery – Cc Submission to form user.

When I set the form to send to my domains email I have no issues receiving mail. This is how I have it setup by default since the form submissions come into me but when I want to Cc the submission to the user using the Mail2 option my success rate of delivery has not been great. I have tested with a Comcast account and have not gotten any deliveries. I have tried a Yahoo account and it did successfully send the email. I did have to look in the SPAM folder but the mail function did delivery the email. Gmail had zero successful deliveries. 1 in 3 is not so great. Any ideas on how to have a better email delivery success rate when Ccing out a copy of the form?

https://www.ads-software.com/plugins/contact-form-7/