For those who don't want to or can't listen to the podcast. I've only listened to about 2 minutes of the relevant part, so I'm certainly no expert.

Paraphrasing; Thunderbird Send is basically a large file sharing service for email. All is encrypted. It's not recommended to send decryption password via the same email as the file, unless it's a cat photo.

Unknowns/questions I have. Possibly answered further in the podcast.

-will file downloads be opt in - especially for unknown senders, but also if I'm on a hotspot, I don't want to accidentally download a large file over data.

-can it send unencrypted files if needed?

-how well does it play with other email clients?

-how long does data remain on the server?

-can I access/view files I've uploaded and delete them at any time?