Thunderbird

As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements handled by Mozilla.

Thunderbird is a free, open-source, cross-platform e-mail and news (NNTP) client developed by the Mozilla Foundation. The project strategy is modeled after Mozilla Firefox, a project aimed at creating a Web browser.

Fixed:

• Under some circumstances Thunderbird on Mac will send attachments using the so-called AppleDouble format which can lead to problems with mail servers and recipients
• Encoding problems when exporting address books or messages using the system charset. Messages are now always exported using the UTF-8 encoding.
• If the "Date" header of a message was invalid, Jan 1970 or Dec 1969 was displayed. Now using date from "Received" header instead.
• Body search/filtering didn't reliably ignore content of tags
• Inappropriate warning "Thunderbird prevented the site (addons.thunderbird.net) from asking you to install software on your computer" when installing add-ons
• Incorrect display of correspondents column since own email address was not always detected
• Spurious 
 (encoded newline) inserted into drafts and sent email
• New email not inserted in correct sort order in threaded unified view or search folder