Block free email addressses for PDF download after form submit

I’d like to block free email addresses such as gmail, hotmail, yahoo, etc. from receiving the downloadable PDF we offer after the form submits. I have seen some code floating around that does this to block the actual form submission but not for the download feature. I am using, on_sent_ok: “location = ‘https://www.example.com/mypdf.pdf’;” in the additional settings field. We just do not want this pdf to go to any email addresses with free email accounts. Does anyone have a solution for this?

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