First of all congratulations on a great looking app. I just set it up for my work account (I use a different provider for my private mail) and I love how I have all labels available. I'm also excited that you'll distribute it via the Mac App Store.

My job these days is heavily email based, it sometimes feels like all I'm doing all day is jump between gmail, Slack and Zoom. Thus I've spent a lot of time optimizing my workflow with labels, etc. Unfortunately, I also rely on a lot of integrations with 3rd party services (through Chrome plugins):

- Salesforce - Calendly - Grammarly

If push comes to shove I can do without Calendly and maybe even without Grammarly but its entirely impossible for me to do my work. I dream of an email client like this but the unfortunate reality today is that anything not (easily) connected to certain other services is in a tough position for email power-users - or just people in weird jobs.

Good luck. I'll keep an eye on Mimestream. Maybe at some point there'll be a plug-in API and an opportunity to bring some 3rd party services into the app.