Thunderbird Pro will apparently be:

This email thing plus Thunderbird Send (which is basically https://send.vis.ee/), Thunderbird Appointment - a scheduling tool and Thunderbird Assist, which is:

"...at least for now, being cautiously labeled as “an experiment” that will allow users to take advantage of AI features within their email. However, the goal is to be lightweight enough that the language models can be run locally on a user’s PC in the interest of privacy. This service is being developed in partnership with Flower AI, which leverages Nvidia’s confidential compute to provide private remote processing in the event a user’s PC isn’t powerful enough. Sipes emphasizes that any remote processing features attached to Thunderbird Assist will always be optional, in the interest of ensuring complete user privacy."

So AI shit that nobody asked for or wants.