Does anyone know of a good resource on how to ramp up onto DNS? I'm afraid DNS is one of those things that everyone learns what's an A record and CNAME record, but once that's set it's just abandoned and forgotten.
I think the Wikipedia article is quite good, and I'd also encourage you to experiment with the "dig" tool, it shows very valuable low-level information, which goes well with the theoretics on Wiki.
You can also play with DNS by registering a domain name and running two VPSs as nameservers. I also run my own mail server and find this setup amazingly convenient.