I don't think so, I believe open relays are virtually extinct. People rarely run MTAs those days, and default configurations are quite protective. And if someone still manages to mess it up, they're gonna get famous with all the RBLs in days if not hours.
I self-host my mail for over 17 years. Most of the spam I'm observing those days comes from hacked/broken websites (sometimes it's probably some stolen SMTP credentials, sometimes sent from the server directly). Legit domain name, SPF and even DKIM present, looks totally legit in this regard - only stopped by RBLs and content filtering.
I self-host my mail for over 17 years. Most of the spam I'm observing those days comes from hacked/broken websites (sometimes it's probably some stolen SMTP credentials, sometimes sent from the server directly). Legit domain name, SPF and even DKIM present, looks totally legit in this regard - only stopped by RBLs and content filtering.