The top two landing places for Thunderbird: The Software Freedom Conservatory, a U.S.-based nonprofit that centralizes funding and provides infrastructure for more than three-dozen open-source projects; and the Document Foundation, a German nonprofit whose best-known project is the LibreOffice productivity suite.
The Mozilla Foundation was a third possibility, according to Simon Phipps, a noted open-source expert, who was hired to identify the best organizational destinations for Thunderbird.
Phipps' report, which was released Monday by Mozilla, was one result of the decision in December 2015 to untangle Thunderbird's and Firefox's development, under-the-hood technologies and hosting infrastructure.
Mozilla stopped directly supporting Thunderbird in 2012, when the foundation shut down the email client's parent, Mozilla Messaging, and handed coding responsibilities to a group of volunteers. But it wanted to separate the two even further.
"Firefox and Thunderbird have diverging needs," said Mitchell Baker, the chairwoman of the Mozilla Foundation, in December. "Firefox needs to move at the speed of the Web ... [and] Thunderbird is a valuable and respected open source project, with different parameters."
Since then, Mozilla split the separation process into two parts: Finding an organizational home for Thunderbird and dealing with the technical aspects of the divorce.
Phipps' report also discussed other groups as potential homes for Thunderbird, including the Apache Software Foundation and the GNOME Foundation, but he pointed out that the former may be unsuitable because of its funding practices and that the latter had passed on the idea.
The Software Freedom Conservatory was willing to host Thunderbird, Phipps said, but the Document Foundation has deferred a decision.
Mozilla has also made progress on the technical half of cutting the cord to Thunderbird, including advertising for a technical architect, who will identify issues and make recommendation to the Thunderbird volunteers on how to migrate from Mozilla to a new home.
In a post to his personal blog, Mark Surman, executive director of the Mozilla Foundation, offered a bit more information on why the organization was searching for a new Thunderbird abode. His explanation: Thunderbird was holding back Firefox.
"If we want Firefox to continue to have an impact on how developers and consumers interact with the Internet, we need to move much more quickly to innovate on mobile and in the cloud," Surman wrote. "In contrast, success for Thunderbird means remaining a reliable and stable open source desktop email client."
The job description for the technical architect was even clearer, and also hinted at other changes Mozilla may make to its browser, including switching to the Chromium rendering engine, which powers Google's Chrome. "Thunderbird has tried to maintain its practice of being based on the latest version of the shared Gecko codebase," the listing stated. "However, in 2016 we find this is both putting pressure on Thunderbird's limited resources and slowing down Firefox -- and this problem is going to increase in the short term as Firefox prepares to make some larger breaking changes."
Thunderbird, which runs on Windows, OS X and Linux, can be downloaded from Mozilla's website.