It's been hashed out in here before, and no, there is nothing in the RFC mandating the it reverse resolves.
Just my $0.2, but I tried doing exactly that for awhile but stopped because it was blocking more legit mail than spam. There are a lot of badly configured DNS servers out there.
Jeff Garvas wrote:
Does anyone know why the SMTP server for this list doesn't reverse resolve?
I'm thinking of turning on mandatory reverse resolve to cut down on the volume of junk hosts connecting from 22.214.171.124/8 and I noticed that doing so would stop delivery from this mailing list.
Does anyone know if reverse DNS of a connecting SMTP server is outlined in any of the SMTP RFCs?
If so, I'd like to reference the RFC in my error message.