Check out
Mutt and
Alpine – two superb command-line e-mail clients. You could run either or both in a FreeNAS jail, and use SSH to log in to the jail and check your messages.
Mutt is very feature-rich, but also quite complicated to set up, though there are tutorials and configuration tips all over the web. Alpine is simpler, and perhaps a better place to start if you're not totally comfortable in a console environment. To make an analogy with text editors, I would say that if Mutt was
emacs or
vi, Alpine would be
Nano or
Pico.
Those are my favourites, but there are plenty of other jail-friendly command-line mail clients listed on
Wikipedia. If you'd rather have something with a web front-end, you could even set up a jail-based web server with an
AJAX or PHP webmail client and check your messages with a web browser.
I recently dropped Apple Mail in favour of Mutt, and run it on my Mac laptop and on a home FreeNAS server in a standard jail. The jail has all my favourite BSD command-line tools and configuration options set up as a cushy home development environment. The advantage of setting everything up in a FreeNAS jail is that it's always on and able to run prolonged or automated tasks, unlike a laptop or phone. I can access it from my home LAN, or from anywhere in the world over SSH or VPN thanks to
tmux and a
pfSense router.