I think they only block /16 or maybe /24 blocks... Meaning they block entire ISP networks... What I do is to simply sign up to many cheap VPS until I get an IP

I think they only block /16 or maybe /24 blocks... Meaning they block entire ISP networks... What I do is to simply sign up to many cheap VPS until I get an IP that is not blocked... Then relay all e-mails via that server. I guess spammers have the same tactic, but it does work.