I've been donating to Thunderbird the past few years when it started accepting donations just for it (instead of being a donation to Mozilla though Thunderbird was spun off as a community driven project with some support from Mozilla).

If Mozilla comes with a paid email service focusing on privacy that's not just a white label rebranding of ProtonMail (which I won't use) or another existing provider, I'd surely be one of the first to try it out. Something that's preferably cheaper for multiple mailboxes with own domain support would be awesome.