I never used residential IPs. Most ISPs don't even let you set PTR records on those. My problem was that any server at practically any provider would reuse an IP that previous customers have used to send spam in the past. For example you can't hope to send mail from a DigitalOcean IPv4 address without going to spam. Nor from Kamatera. There are probably a few more providers that are basically blackholed because they're so often used for spam. (I don't have experience with providers that don't offer IPv4.) I believe some providers even attempt to block outgoing mail.