Unbannable IPs

There is no unbannable ip's, even microsoft's or yahoo ips are blacklisted, specially yahoo since many spamming through these.
Any ip's that are spamming will get blacklisted. There are some whitelist directories that you can pay but again if you are spamming you will get blacklisted as well.
The only you can do as precaution measures is to setup correctly your mail server.
Check that your reverse dns matches your smtp banner, that you have setup correctly an spf record in your dns and that you relay your mails via different ip's (load balancing), and of course that your mail server is not an open relay one.
Even if you ensure below it does not mean that your ip's will not get banned, but it would be much more difficult to do so.

All addresses can be banned, and will be, in the end there will be no unbanned ip addresses

unbannable ips, dude u kidding? google is here watching us all, all the time, you can get banned anytime doing illegal so you just have to jump ip after ip