procedure/protocol for ensuring the decency of a new IP address

Solution 1:

IP-address “reputation” is as far as I know only a concern for reliable e-mail delivery.

You can easily find online query tools for such as https://mxtoolbox.com/blacklists.aspx for public blacklists. If your new IP-address is listed in one or several that is probably a bad sign but when it is not, then there is no guarantee that it’s history is good either.

If your IP is listed in a blacklist you may see it disappear automatically or there may be an appeal procedure where as the new operator you can request removal.

Since a clean inbox is quite an important competitive edge most of the large email providers don’t disclose how they achieve that, although they certainly won’t rely on public blacklists alone (or at all). In the end you can only determine if your messages will arrive in the intended recipients Inbox by sending them messages.

Before you start sending mail : configure your server correctly by reading these related Q&A’s

How to send emails and avoid them being classified as spam?

Prevent mail being marked as spam

If you have neither the time or resources to build up a good sender score (when you relative frequently switch providers and/or change IP-address) consider using a transactional e-mail provider to avoid that hassle.