Web & Mail Server-Mirroring,Clustering ?

I am wondering if there is a solution to switch the web and mail server from the first location to another server in different location (different IP of course) but with the same domain name in a short period of time if the first server is down, so that the email server continue to operate.

I was told Clustering works only on the same location placing both computers side-by-side, physically connected with ethernet cable. What about ADSL line to another ADSL line with Static IP?

Thanks.