Mozilla Thunderbird is an open source, cross-platform email, news and chat client developed by the Mozilla Foundation. On July 6, 2012, Mozilla announced they were dropping the priority of Thunderbird development, pointing out that the continuous effort to extend Thunderbird’s feature set remained mostly fruitless. The new development model is based on Mozilla offering only “Extended Support Releases”, which deliver security and maintenance updates, while allowing community to take over the development of new features.
