Betygsatt 5 utav 5 stjärnor

I originally left a negative review because I hadn’t understood that scheduled messages are only sent while Thunderbird is running. After actually reading the documentation, I realised this is a technical limitation that the add-on never claims to solve – and that the author even explains in detail, including alternatives for offline sending. The extension itself works very reliably and is thoughtfully designed, so I’m updating my rating to 5 stars. Thank you for providing and maintaining this add-on.

It's documented in the user guide. There's a whole section there about alternatives if you need something for sending scheduled email when you're offline.
It is not appropriate to give a 2-star review because an extension doesn't do something it isn't designed to do.