The netblock thing has happened to me. My Linode that I’ve had sending mail for 6 years gets blacklisted now purely for being on the netblock that it’s on.
Re:Don't send to Gmail over IPv6
by apocalyptic0n3 on Friday June 03, 2022 @04:40PM
(#31613357)
Yep. I've encountered the exact same issues on multiple Linode servers in multiple data centers. I've also experienced it with an AWS server. It's often almost impossible to get it unblocked because the support teams at the email providers (if you can even contact them) don't realize that's what's happening. I didn't understand it myself until I got a call with an engineer at Microsoft who realized it in the middle of our call. He unlisted us on the call and we were fine for a while, but were eventually blocked again and haven't been able to get unblocked. It's really frustrating and I'm slowly ending all of my email services (both professional and hobby) as a result.
It’s frustrating. I had outbound smtp throttled right down and a script running that shut smtp down completely if the queue got too big. That triggers an alert and everything gets sorted. But no, we don’t like where you’re from so jog on. Monopolistic.
while I concur with all of the points you make, there is a logical and statistically accurate reason for some of these spam filters.
even if your no-open-relay, rdns, spf, dkim, dmarc, SSL/TLS and other configuration is absolutely impeccable on your smtpd, your only recourse in a situation like this is to change to a new ISP that does not have a poor IP space reputation in all the adjacent IPs.