Need some advices for Failover - High-Availability

[pattone]

First of all sorry for my english (I'm from argentine)
I have a server wich I setup with this great guide http://www.howtoforge.com/perfect-se...ot-ispconfig-3
and is working great with a few websites and domains. Now, looking for information for setup a second server (for failover purpose) that will be in another phisical place with another ip and internet connection I found this 2 excelents howtos:
http://www.howtoforge.com/setting-up...n-debian-lenny
http://www.howtoforge.com/setting-up...n-debian-lenny

and I was wondering what about mail server; my server actually have a few domains with somes mails accounts and I want to have a second server not only for web sites, I want a failover system for mail too. Is there a way to setup this??

Thanks in advance