Thundercast is a great listen! Its not all about mozilla stuff either. Mostly a group of thunderbird team members hanging out with a few discussion topics.

Sounds like it will probably be behind a subscription like Firefox Relay and Mozilla VPN, and probably very affordable like those. Server costs and all.

Definitely looking forward to more info about this. I really enjoyed the original send, and solving large files in email without needing to wire up a webDAV drive or go to another service to upload would be awesome. Presumably it'll be thunderbird focused, but hopefully it can be used from a browser extension or web app to use on the go or with webmail clients too.