I can't seem to select any text on your website so had to go screenshot, then select. But:

> All your devices, synced

> Mac, Windows, iOS, Android-stay in sync across all platforms.

Does this mean email passes through a server like Spark[1]?

[1] https://sparkmailapp.com

Your screenshot looks nice. I hope you succeed with this, and I'd be happy to try it. From what little I know, building a fully-compliant IMAP client is hard work.