Ok, so far so good, and it appears to be working, but am I right in assuming that this will only stop email from those countries? What I need is a way to block them from my server full stop!
Not quite sure what you mean.
Your server will not accept mail from countries in your Geoip config.
Blocking full stop? Do you mean block from making a connection in the first place? That's a different ball game altogether. First, it isn't really necessary if your server doesn't accept them. It's really just aesthetics in your logs.
If you really do want to do more look at fail2ban with a custom script, and I think elsewhere here look for xtables which I think now works with geoip2