Suppose you have the domain
yourdomain.com, and you have set the following SPF:
v=spf1 +ptr:yourdomain.com ~all
Now, I have the IP address 18.104.22.168, and I am also the administrator of
3.2.1.in-addr.arpa. I can specify
4 IN PTR fake.yourdomain.com.
and then I can send emails from my machine, pretending it's one of the
Is this a significant risk? Should I avoid using ptr in the SPF?