Forms - customer not receiving "Thank You for submitting" email

Hello,
I did numerous tests on the forms within a website when it was offline. Everything seemed to be working well. Email notifications were going to both the admin and the customer properly. Today the website went live and I did some tests on the forms again. The admin gets the notification email, but the customer does not. Through the design process the forms were tweaked a bit with color changes, inputs, etc. but nothing was changed for the submission info. I can't figure out what happened. I am not sure whether it has to do with the FROM EMAIL (Now showing CUSTOM in the attached image). Should it be on default? I did not manually change this from when the forms were working. Most of the forms on the website are lightbox and every time there is any revisions, I need to make the change, save, duplicate the form, delete the old form, and input the new form number into the class suffix. This is the only method I could figured out to make adjustments to forms once they were attached to a button. When I just saved the changes, they were not being updated. I don't want to go through this again on all the files! Lol!

Thank you!

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