Don't use Thunderbird.

Look at either ditching Ubuntu for Debian if you like that sort of thing, and, at the very least, get KDE installed and use Kmail. It looks more like Outlook than what you have. Kmail, TKrat f you want to rock it old school, and Gnumail... There's also a few more, like, I think 70 or so email apps you can pick from, but most people will stick with known apps. I personally Use Opera, Kmail, and Sylpheed. You may like Sylpheed / Claws, because it works really well, and it's fast and has very little in terms of resource needs.

Actually, just get Kmail and Sylpheed. There's a related app to Sylpheed which you can read about by basically just looking up Sylpheed. Ubuntu should have a package for it, and if not, use the Debian one.