Mail options

I thought I'd do a post about open source email options for OS X as this is something I've not yet covered.
There are a couple of options for mail. The most obvious option would be apple mail, but of course, this is not open source.
I guess the most obvious open source choice would be Mozilla's Thunderbird. This is an excellent client. I used to use it a lot, back in the dark days when I used Windows. It has all the things you would expect from a modern email client and it also features add ons and plugins just like firefox.
For those of you who don't mind the command line, two of my favourite clients are Mutt and emacs/gnus (which is what I use primarily). Mutt can be a bit fiddly to set up but is very good especially if you are running your own mail server. Again, gnus can also be a bit of a nightmare to set up, especially if you want to use SSL connections to retrieve your mail, but I just like using emacs to write my mail.