> On 16 Jul 2016, at 02:50, Lefteris Tsintjelis <le...@spes.gr> wrote: > > I was thinking it more in simple DNS terms only and a simply reverse > look up of the IP and then extract the domain from there but it is not > possible without the FROM.
That wouldn’t have worked anyway. Assuming a reverse lookup of an IP address returns a name -- a big if -- there’s no guarantee that name has any relation to whatever domain name is in the MAIL FROM. For instance, lots of organisations outsource their email to specialised hosting/service providers. A MAIL FROM might well say example.com while the reverse lookup returns some name in $emailprovider.com for a server that’s delivering email sent by bazillions of customers.
