What email client was originally codenamed Minotaur?

Mozilla Thunderbird was originally codenamed Minotaur.

Minotaur began as a Mozilla mail-client project in 2003, developed alongside Phoenix, the early name for what became Mozilla Firefox. The project initially struggled to attract momentum, while Phoenix gained attention as a faster, simpler browser.

As Firefox became successful, demand grew for a compatible standalone email application. Mozilla revived the mail project, moved it to the newer toolkit used by the Firefox team, and renamed it Thunderbird. The new name therefore refers to the revived successor, not an entirely unrelated product.

Thunderbird 1.0 was released on December 7, 2004, and passed 500,000 downloads within three days and one million within ten days. A common mix-up is confusing Minotaur with Phoenix: Phoenix was the browser project that became Firefox, while Minotaur was the email project that became Thunderbird. Later Thunderbird development also used codenames such as Shredder for early Thunderbird 3 releases.