For SPF to answer the question, domain owners have to designate which IP addresses send mail for their domains.
For example, hotmail.com would publish a SPF list that includes 188.8.131.52, 184.108.40.206, and 220.127.116.11, which are all servers which you could reasonably expect to see a hotmail message coming from. But if someone connects from 18.104.22.168 and claims to be a hotmail sender, you would know better than to believe them, because that IP address isn't on the list.
There is not "ID" being sent. It's DNS authetication.
So instead of 500 spam a day, you get 500 caller ID alerts a day..lol
It's not the spam contents itself that bothers me, it's the time I have to take to delete it all... I wish I could simply delete the junk I get in my snail mail box though... I know what I will do, divide my mail box in half. Tell the postal worker "Mass mail here, personal mail and ,ugh, bills, here.. There's an invention that needs creation...heh