You wrote: "...many legitimate mailserver IPs have a reverse DNS entry that looks a lot like a dynamic IP (often the exact same format as a dynamic IP from the same Internet provider)."
I can't prove it, but I --think-- these are default PTR records that ISP's have installed covering their entire IP blocks, something like "*.3.2.1.in-addr-arpa" so that all their customers' IP's have a response for RDNS without them having to manage them inidividually. This practice just makes the spam problem worse, as it has the net effect of making every IP look like it's got a mail server hooked up. Either that, or the ISP's just wrote a one-time script that populated all their IP's into their reverse zone files with cooresponding PTR values of "4-3-2-1-cust.someisp.tld" (matching customer IP of 1.2.3.4) which does the same thing and is still wrong. Yes the record is there for systems that check, but it's wrong in content, and at least here we add score for matching patterns like that. IMHO (which may or may not bear any merit) if ISP's are going to allocate IP's they also need to allocate the DNS responsibility for those IP's to the customer and allow (force?) the customer to serve DNS records themselves, or at least convert thier authoritative zones to slave off the customers' DNS server so the customer has control. I know you're all gasping out there, and that there are a lot of small companies that have decided they want in-house mail only and not the rest of it for lack of expertise in network management, and for those it's the ISP's responsibility to educate and work cooperatively with the customer to make things right and keep them right. Chris To Unsubscribe: http://www.ipswitch.com/support/mailing-lists.html List Archive: http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/
