Mozilla Thunderbird

Permanent link Thunderbird 3   

• Great smart view mixing accounts.
• Multithreaded email and IMAP caching and management.
• Sum-up of discussions.
• Tabs.
• Most Thunderbird2 plugins are compatible as long as one disable version checking.

Permanent link Good plugins   

• quotecollapse which can be customized: partly hide quoted discussions when they exceed some length.
• Nostalgy: manage emails storage/copying/moving through keyboard shortcuts
• ThreadBubble: sort discussions by latest messages
• Adblock Plus: anti-ads
• Lightning: calendar and agenda
• Url Link: select and open long multi-line URL
• Silvermel, gorgeous theme.
• Newsgroup Links: add links in newsgroup discussion to Google Groups.