Secondary Mail Server - Clone/Slave

[kaotix]

I have recently setup a secondary (slave) DNS server for my ISPCP panel and it is working perfectly. I followed the guide on the wiki but the script it uses was basically terrible.
I recoded the script that downloads the new zone file and it works flawlessly on my production server.

I would like to now do the same for my mail server as the secondary DNS server is capable of hosting the mail as well. I have no idea how to clone the mail server which is my main problem. My main reason is that I often have to take my main server down to perform updates and the mail server is one of the main things that people ask for during this period.

Any help would be appreciated.
Thanks