Foundry376/Mailspring ? reverse-engineered prompt

Build me a polished desktop email app like Mailspring that works on Mac, Windows, and Linux. I want it to feel fast and light, with a clean inbox, unified inbox support, snooze, send later, mail rules, templates, and a composer that feels modern and easy to use. It should connect to regular email accounts locally, keep everything private on the user’s computer, and not send credentials to the cloud.

Please make it extendable with plugins and easy to theme, since that is a big part of the app. Use the existing open source style and make sure the app runs well from source, with a good developer setup and sensible defaults. If you need to check current docs or best practices for Electron and TypeScript, feel free to look them up online as you go.