While learning about various e-mail anti spoofing techniques, I’ve come to wonder about the apparently once common requirement of reverse PTR DNS entries to make sure a server isn’t a spoofing one, and DKIM.
It made me wonder, doesn’t DKIM kind of render reverse PTR DNS entries redundant? Do common big providers still require reverse PTR names for mail servers in practice when DKIM is present? With big providers I mean Google Mail, Microsoft’s Outlook Mail, and so on. It seems to me like a valid DKIM signature would render that check redundant, while also many ISPs don’t seem to offer reverse PTR entries while a DKIM signature doesn’t require any special ISP involvement.
As a result, it almost even feels like the e-mail ecosystem would be kind of made worse by still enforcing reverse PTR DNS in the presence of DKIM.
Or am I missing something here? I’m curious about in-depth responses.
