Jed Smith wrote:
Depending on the chain of delegation, a server operator may not have access to modify his PTR record and might not be able to change it.
It's a common belief among network operators that if a "server operator" doesn't have access/ability to modify the PTR record for a server, it's a good sign that the server shouldn't be used to send email, but instead should send email thru an email server provided by their upstream access provider. The people who manage those servers, who can't or won't fix the PTR *or* send email thru an email server provided by their access provider, think it is critically important that the rest of the internet receive their missives. They are mistaken. Their missives come from "a bad neighborhood" (IPs with PTR formats that are strongly associated with botnets) where the odds of any email being desired by the recipient are extremely low. If they want their email to avoid being treated as spam then they need to move to a better neighborhood (fix the PTR) or send from a server located in a better neighborhood (a server with a correct PTR for a mail server). Endlessly whining "I wanna, I wanna, I can't, You should, I wanna" over and over isn't going to change anything. Other networks aren't going to change how they filter based on PTR for someone who can't properly assign the PTR for their mail server. jc