All those Conservative paid medias like newsmax (the worse crazy stuff) send out sometimes 15 emails a day. I don't know how they get away with that kind of spam but they do.
If you can show your Dad how to click on the bottom and un subscribe he will get less emails. Better yet have him abandon his current email address and start a new fresh email. never give them your email address.
I've taken a email address and signed up just for a couple like newsmax, to see what would happen. It went to over 200 emails a day within a month.
My family has several in the military, some Navy and plenty who served in the Army. Thank you for serving and be safe!