There are several low-cost low-cost options for a personal server. Since Confidant Mail makes it easy to move your account from one server to another, where to host is not a high-stakes decision.

Used/Broken Laptop

Laptops are quiet and power-efficient compared to desktops. Used laptops can often be acquired free or nearly free with dead batteries, broken displays, faulty keyboards, etc. while the CPU and hard drive are functional. Attach an external display and keyboard to set up the machine. Once set up, just place the laptop next to your broadband router and control it remotely. You can either install Linux and use SSH administration, or keep Windows and install TightVNC for remote administration.

Amazon EC2

You can get one year of free service on Amazon EC2. The Free Tier machine (t2.micro) can serve several users.

Raspberry Pi

The Raspberry Pi is a single-board Linux computer, which can be used as a Confidant Mail server. Compared to a regular PC, it has some advantages. It is small and silent, power-efficient, and the whole system costs under $60. In addition to being a Confidant Mail server, it can also do things like serve files from an external USB drive, download torrents, and run a VPN.

Purchasing information and software download links are here:
http://www.raspberrypi.org

You will need the B+ model, which costs $30 and includes Ethernet. You will also need a case, an SD card for storage, and a Micro USB cell phone charger for power. For initial setup you need an HDMI display and a USB keyboard. After installation, you can manage the device remotely by ssh.

These instructions are for Raspbian September 2014.