[Soekris] Ideas to build bullet-proof firewall/SMTP server using net4801?

[Frank Tarczynski]

I'm going to be traveling for an extended period of time and will need a 
rugged SMTP server to collect my mail with minimal heat generation/power 
consumption that I can cable-up directly to my cable modem.

I've got a net4801 currently serving as an astlinux box that I can use. 
  I can add a hard disk to my net4801 and plug it in to a large UPS for 
power back-up.

I'd appreciate any thoughts or pointers.

Frank