Hello Michael,
Spark e-mail client from Readdle recently arrived to macOS. I installed it and it is nice e-mail client. Cannot figure out if it even is scriptable though. Would you look at it when you have chance and see how much EF can support import of e-mails? Capability to import e-mails into EF is basically required for my e-mail clients as I just keep filing e-mails in EF libraries. For now I work with Mail.app, but damn, that thing is getting old and obsolete compared to others. Even when extended by various (expensive) extensions (e.g., Mailtags).
No rush… I have little hope.
Thanks a lot!
Jan