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.
- Message preview pane non-functional after IMAP folder was renamed or moved
- "Move To" button on "Search Messages" panel not working
- Message sent to "undisclosed recipients" shows no recipient (non-functional since Thunderbird version 38)
- Calendar: No way to accept/decline email invitations when sent and received messages are stored in the same folder
- Various security fixes
- OS X 10.6 or later