Thunderbird is a FREE, opensource program. No donation is required to download, install, or use it, though it is appreciated by the developers.

Be sure you are downloading it from the official source, not some scam cite.

https://www.thunderbird.net/en-US/thunderbird/all/

Hi Meg,

People sometimes report that the download did not happen, but they are just not looking in the right place. Have you looked where your browser is set to save downloaded files?

Of course, there will be a message about downloading each time a person downloads. The download site doesn't know what you have done in the past.