Contact Form 7 failed to send

I’ve used Contact Form 7 with GoDaddy hosting previously without a problem. But this time the form works on some computers and on others we get the “error not sent” red-lined message. This is the only WP site I’ve done using Windows hosting. I have both Mac and Windows computers and the forms work just fine. Some others have no problems as well. But two of the clients (using IE on Windows) get the “error not sent contact administrator” message. I’m using CF7 for four different forms and need it to work. Any clues as to what the problem is? I’ve looked thru previous posts, many of them were not answered and closed on the first question.

https://sewingreferralnetwork.com/contact/ is just one place I’m using the form.