• Mozilla Thunderbird

From author's site:

Thunderbird 2 features many new enhancements to help you better manage your unruly inbox, and stay informed. Thunderbird 2 scales to the most sophisticated organizational needs while making it easy to find what you need.

Mozilla has bolstered Thunderbird’s acclaimed security and privacy measures to ensure that your communications and identity remain safe. It’s like having your own security guard online.

Thunderbird allows you to customize your email to suit your specific needs whether it’s how you search and find messages or listening to music right out of your inbox.