Given that you talk about 'even' implementing SPF, and now about IP blacklisting gives me the impression you haven't actually worked (or kept up with) email ove

Given that you talk about 'even' implementing SPF, and now about IP blacklisting gives me the impression you haven't actually worked (or kept up with) email over the last 10 years. None of the major email service providers (or 'behemoths', as you call them) use IP blacklisting anymore. They abandoned that idea years ago. IP addresses are ephemeral, especially when IPv6 is used, so IP blacklisting simply does not work anymore. If we were to use IP based blacklisting we'd have blacklisted the entire IPv4 address space by now. Yes, like any other SMTP service they will block IP addresses momentarily if you misbehave, but never permanently. All major spam filters are content based, and reputation is always on the domain level, not IP level. If you properly configure your email infrastructure, and you don't spam, then deliverability really shouldn't be a problem.