I had emails returned due to no reverse address. My email server is running on one of my VPS and I have had all my VPS DNS delegated to me as well. I have been using the email server since the dawn of time, this hasn't happened before.
Now after a lot of digging, these servers that rejected said no rDNS on the IPv4 address (There were infact 2 of them UKmail and BTInternet.) I think it is because they are querying the Bitfolk servers, because, of course, I only have the one IPv4 address delegated to me and they are looking for the IPv4 reverse address of Keynesmail.com at theBitfolk server. It doesn't know about that domain name - no reason it should really.
So should I ask Andy for secondary DNS for that domain name, would that solve the problem? Or is there another way out of this. I have a number of very low traffic domains on that VPS, but this one domain, that of the email server is causing this heartache.
I guess those 2 are the only ones we have come across using IPv4, all other addresses sent to just work fine, including Gmail and Yahoo mail. The email address having problems with the sending is one used by a small local cancer support group and both the user of it and the intended recipients are total technophobes as well as being, like me, rather advanced in years.