Thunderbird

"Thunderbird makes emailing safer, faster, and easier than ever before with the industry’s best implementations of features such as intelligent spam filters, saved search folders, built in RSS support, privacy protection and much more."

Thunderbird offers intelligent spam filters as well, which can greatly increase your security as well as reduce the clutter in your life. It's the client that I use every day.

Paul Thurrott wrote a thorough review of Thunderbird 2.0. One thing will be clear if you visit his site: The man can write.

Key Thunderbird Places

Thunderbird security

From the Thunderbird FAQ:

Thunderbird will not allow a virus or worm to execute automatically. You can see what attachments have been sent to you without a virus being able to execute, and you would have to save a file to your system and deliberately run it before it could cause any harm.

JavaScript is switched off by default for mail and news, so an e-mail cannot run script code just by being opened.

As with any mail program, take proper caution before running any file that you receive in e-mail. Appropriate anti-virus software should also help keep you safer.

Backup

Just back up the contents of your "Profile" folder. It's something like C:\Documents and Settings\Your Username\Application Data\Thunderbird\Profiles\nc8tkzcq\. [more] [MozBackup]

Then replace the entire contents of that folder with your backup if you ever need to. The restored profile will replace your email messages, addresses and settings (up to the date you last backed up your profile. [more yet]

Mailstore gives you a convenient way backup your email on a regular basis. It's an excellent, easy to use program that is free for personal use.