Perhaps if there are no links (or anything that looks like a URL) in the message body, this option could be provided. The default could also be unchecked, with some brief explanatory note, along the lines of "if this spam email is trying to solicit direct replies, rather than clicking on links, you can report it to the provider of the account that would receive such replies".
I'm not so sure. About 96 hours ago I manually I sent a buch of these such emails as specimens to firstname.lastname@example.org. I was getting about 2-3 a day. I now haven't received any in almost the last 48 hours. Fingers crossed.
I know. Often they had the Gmail address before the website, and to have two email addresses seems a complexity beyond them. "But I can set up forwarding for you." "Too complicated." "An email account @yourwebsite will look more professional." "I'm doing fine. I just wanted a website, that's all."