Compact solution with external hard drive?

Hello

Some non-techie people I know rely on mailing lists to share infos for their non-profit organization.

As a better (to me) alternative, I'd like to find a compact, Linux-based embedded solution to run a web-based forum, probably SMF, FluxBB, or PunBB.

Those are low-traffic lists, so it could sit at someone's home and share their ADSL connection.

The requirements I could think of:

• Passively-cooled, flash memory-based server, à la SheevaPlug
• Can take an external hard drive to hold the forum's data, as hard drives offer more bang for the buck than eg. SD cards
• The forum should be dead easy to use, back up/restore, and upgrade when new releases are available.

What hardware would you recommend?

Thank you.

First choice: Beaglebone Black
Second choice: Raspberry Pi

I use a 5$ digital ocean cloud VM for my mail relay.

Thanks. I'll check out the different models available from Beaglebone.