This page adds detail to the troubleshooting SMTP peers page for the following topics:
On 18/Jul/2011, TFN removed the reverse DNS requirement for SMTP peers. Our reasoning was this:
Far too many hosts, primarily from small & medium-sized, local companies, have incorrectly configured DNS but have legitimate correspondence to deliver to TFN members. The fact that we were rejecting that email was a perpetual source of grief. Problems took long to resolve because it was difficult to reach the technical staff of such companies and even more difficult to convince them of flaws in their work.
Some of TFN's competitors were more forgiving, and were accepting email from misconfigured sites. This made it seem, to our members and to their correspondents at those sites, that the problem lay with TFN.
Aside from these false positives, the absence of reverse DNS was an effective way of identifying spam early. Without this check, we are forced to absorb much larger spam volumes inside our gates, but at least complaints about rejected email have stopped.