[SahAssar]

> floated the idea of using Stawart as the "server" implementation of JMAP and using something like mbsync to sync IMAP from their mail provider. And build a client on top of this Stalwart "server."

That really does not seem like a workable solution. It would probably be brittle, require double the storage, require mapping of accounts and and credentials, would not account for caldav/carddav, etc.

If JMAP is to take off we need proper clients, servers and bridges. I'm not sure we even have one proper OSS implementation for each.