You need control of the entire netblock you send email from. Everything was going smoothly for me for 7 years until the entire Digital Ocean netblock my static IP was in landed in a permanent blacklist due to enough of the other IPs in that block having repeated complaints. I don't remember the mailing blacklist it was on but unblocking that single IP required the netblock owner (Digital Ocean) contacting the blacklist provider directly
this is why persons self-hosting email servers are much more likely to have success using a small to medium sized, trusted local ISP where you can establish a relationship with the persons who run the ASN. And determine for certain that the ipv4 /24 your mail server's /32 is contained within does not contain random other $5 to $30/month people buying VPS/VMs/low-budget-dedicated-servers with credit cards.
If you can have a high degree of confidence that no outgoing smtp spam traffic has ever been emitted from any of the other IPs adjacent to where you're hosted, the opaque blacklists of the big mail receiving providers (gmail, etc) are much less likely to consider your legit traffic as spam.
