Scalable (incoming) mail cluster

This is one way to build a scalable mail infrastructure. Besides GlusterFS, the performance is pretty good.

"Business Case" for this setup:

• Postfix, because it is written by a Dutchman and it supports the Proxy Protocol. Proxy protocol will preserve the original IP address and forward that to the back-end. The original IP address is needed for DNS-based blacklisting of spammers.
• HAProxy, because it supports/invented the Proxy Protocol
• GlusterFS, because it is a cool way to experiment with a clustered file-system and easy to setup
• Lighttpd, because it is not Apache
• OpenLDAP and Bind are just de facto standard applications