I've had some problems in the past with AT&T/Yahoo accounts receiving email from some personal accounts hosted on resellerzoom (RZ) in which the emails got delivered into their spam folder. RZ was not on any blocked IP list, but Yahoo had a form that RZ could fill out to supposedly resolve this. But after a series of unhelpful responses, I gave up on RZ trying to resolve it and ended up using sbcglobal.net as my smtp server and all was well. (As an aside, this was my only bad support experience with RZ.)
Now I also have business accounts on RZ (different server) and email using RZ's smtp server apparently wasn't a problem for a long while (I think). However I just got an email from a client who told me that email was being delivered to the spam folder. He called AT&T who said that "your ISP and or Domain Service Provider does not currently have a reverse DNS (domain name service) Record for your email or the [ourdomain].com name. Because of this Yahoo's mail servers flag the email as spam." I contacted RZ and they said that the server DOES have reverse DNS (subsequently verified with dnsreports). But I would need to purchase a dedicated IP if I wanted reverse dns for our business domains.
Any idea as to what is going on here? Is AT&T full of it (saying that the domain needs a reverse dns even though the sending server has one)?