@icoso Well, I never used file uploads with any of my forms, but your questions is a good one. So I edited one of my Contact-7 forms to use file upload to see if the file attachment was encrypted. The form sends emails to my Protonmail account, and the attachment seems to have been encrypted. Protonmail displays a green padlock if the email is encrypted, if it’s not, the padlock is gray and opened.
In other words, the email that Protonmail receives is either fully encrypted or not. With all this said, I have yet to test by sending to another account that does not support encryption to see if anything can be read.
I will try that soon and give an update here.