[csnover]

IP range is definitely a problem. I manage to get blacklisted a couple times per year by Hotmail, who still only support IPv4, despite SNDS always saying everything is fine. They don’t seem to care that blocking a whole IPv4 netrange of a reputable VPS provider because some other customer was sending junk mail will cause collateral damage.

IP/domain reputation is also probably an issue; I’ve been using the same IP address and domain names for over a decade so services like Talos are reasonably satisfied I’m harmless. If someone sets up a server and it has never sent mail for their domain before—or, worse, they get a radioactive IP address—it may be hard to become accepted by other email providers.

I get the sense that the relative lack of trouble I have maintaining a mail server is more to do with being effectively grandfathered in and worry that if I ever have to shift away from my current provider that email sending is going to become a lot harder since I won’t have my IP reputation any more.