to quote the Thunderbird.net web site.

Contributions go to MZLA Technologies Corporation, a California corporation wholly owned by the Mozilla Foundation. Funds will be reserved for use in the Thunderbird project. Contributions are not tax-deductible as charitable contributions.

Apart from any other reason there are more than 200 countries in the world, so creating a charity in all of those jurisdictions would be expensive. It might also be because the US does not consider software development to be a charity.

Okay, thanks.

Hello, parkhurs! Thanks for your question.

Since Thunderbird moved from under the Mozilla Foundation to the MZLA Technologies Corporation, it is no longer a nonprofit entity, and therefore not a charity. To read more about this transition--why it was made, what it means for the future of Thunderbird--please check out this blog post from January: https://blog.thunderbird.net/2020/01/thunderbirds-new-home/

As for the contribution appeals you're still seeing, Thunderbird’s funding comes almost exclusively from the generosity of our users, and so we do have donation appeals on our website and on the default start page of the client. However, all donations are entirely voluntary.

We want to protect the privacy and data that belongs to our donors, which means we limit how much "tracking" information and data we send across systems. This protects your sensitive data, but also means we can't customize the Thunderbird start page once you have donated or decided not to donate.

If you would like to customize your start page (for example, to get rid of the donation appeal on that page) please visit: https://support.mozilla.org/kb/how-disable-or-change-thunderbird-start-page

Tl;dr: No, we aren't a charity, but we are almost entirely donor-funded and would appreciate any amount of support. :) Thanks for your question!