Standard IMAP and SMTP — any provider, no lock-in. OpenPGP built in, not bolted on. Native SwiftUI, not a browser wearing a window frame.
Any provider that speaks the protocol — self-hosted, iCloud, or otherwise. No proprietary API required.
Verification and encryption live in the core, not a plugin you install and hope keeps working.
SwiftUI, not Electron or .NET. Fast to open, light to run, feels like it belongs on your Mac.