Thundermail is a great idea! I'd be more than happy to switch over assuming the migration path from say Gmail, Fastmail, etc was easy enough, and it supported custom domains.
I think the synergy part is what is great here. Imagine thundermail is a FOSS server app. Imagine they implement things like proof-of-work for senders, and no PoW means the mail goes into a quarantine instead of directly in the user's inbox. That could fight spam, without the centralization and loss of privacy we've had in email. That hasn't happened now, because of the chicken-egg problem. There's no client that supports it because there's no server that supports it because there's no client that supports it.
Thunderbird is a very big client. It could push email forward like nothing before. I may give Thundermail a try. I'd much rather self-host a Thundermail server... one that works around the port 25 block on every residential IP. Maybe my self hosted instance could receive messages relayed from the "real" thundermail server on something other than port 25.
The few times I've needed support, Fastmail has responded nearly immediately with the exact info I needed. So Moz would need to demonstrate excellence in customer service before I would consider any migration.
(I know that doesn't directly answer your question, but it does articulate a necessary pre-condition, and one that is hard for businesses entering a new line of service to deliver--although not impossible, of course.)
JMAP is a bonus (other fastmail user here) bjt if I can do custom sieve rules and or unlimited aliases created on demand at (somestring)@customdomainiown.com thst I can then use the sieve rules to put into a folder of the same name as that email address, I would rather give my money to support Thunderbird. Fastmail is fine and all but they are in australia so they live on spyware island and they dont have good native clients in the works like thunderbird does.
Unlimited aliases at custom domains are a part of the offering. Technically, Thundermail supports sieve rules, we do need to come up with UX to expose it to users for management.
I think the synergy part is what is great here. Imagine thundermail is a FOSS server app. Imagine they implement things like proof-of-work for senders, and no PoW means the mail goes into a quarantine instead of directly in the user's inbox. That could fight spam, without the centralization and loss of privacy we've had in email. That hasn't happened now, because of the chicken-egg problem. There's no client that supports it because there's no server that supports it because there's no client that supports it.
Thunderbird is a very big client. It could push email forward like nothing before. I may give Thundermail a try. I'd much rather self-host a Thundermail server... one that works around the port 25 block on every residential IP. Maybe my self hosted instance could receive messages relayed from the "real" thundermail server on something other than port 25.