I really think Windows Live Mail was one of the quite good Email clients, which are kinda free. It's based on Outlook Express which I used intensively.
I tried some alternatives (including Opera Mail, Thunderbird, The Bat and others), but neither had all the options I used in OE and in WLM. (multiple signatures, multiple accounts, simple interface, etc).
Note: still have to try em-client, discovered it recently.. SOGo also looks like worth investigating...
Anyways, this post is just about a link to the now almost lost windows live essentials installer package.