Author here. I wanted to build a classic desktop mail client that is self contained (no-proxy shenanigans), small (installer is 4MB), aga has a classic look like Outlook Express had. Used Claude Opus 5.5, the UI is C++, everything else is Rust. Mail protocol handlerd (IMAP, SMTP, MIME) are Rust ports of my Javascript email libraries (Nodemailer, ImapFlow, etc), ported with Claude.