In the past few weeks I’ve been running into more and more references that mail servers are being configured to look at the Reverse DNS entries and if there no entry the messages should be considered spam.
Apart from the fact that I currently don’t have an RDNS entry for my own mail server, I an certainly see the logic in this.
Most fly by night mail servers are going to be setup as quickly as possible. They also want as few ways to track information back to themselves as possible. So RDNS is simply something that they won’t take the time to setup.
The only flaw in this logic comes when ISP automatically setup RNDS on all of their IP addresses. Then any mail server on those addresses is automatically immune to this technique of trying to detect them. The hope here is that they will have to move to another mail server soon enough and that they next ISP won’t have set this up.
I suppose this lends credence to the length of time a domain name has been registered as well. With the basic logic being that domain names that are less then say a month old are more likely to send spam then domains names that have been around for years.
This takes into account that spammers many times just buy throw away domains and never bother to renew them once they come up for renewal.
Another thing to look at on the domain side is how long until the domain name expires. If the term is less then one year the domain name would be less important to the person that owns it then a domain name that will expire in two or five or ten years.
So if a domain is less then a month old and will expire in less then a year the likely hood of the domain sending spam message is quite high in my opinion, but that is all it is … an opinion.
[tag]DNS, Reverse DNS, rdns, spam[/tag]