#What's new

• Ships as MailBoxUltra.app inside a .dmg. Drag into /Applications, right-click → Open on first launch (one-time Gatekeeper prompt). Universal binary; runs natively on Intel and Apple Silicon.
• Native Preferences window (⌘, or the gear button) replaces every --flag: SMTP port, bind address, hostname, max message size, AUTH PLAIN/LOGIN, ring-buffer size, upstream relay URL, NDJSON log file, theme. Atomic JSON persistence in ~/Library/Application Support/com.mpjhorner.MailBoxUltra/settings.json. Apply restarts only the servers whose settings changed; captured messages survive across an SMTP restart.
• HTML email rendered by the system WKWebView — the same engine Mail.app uses — embedded inside the app window. JavaScript is disabled, link clicks intercepted and shelled to the default browser, captured email HTML sandboxed.
• Faithful responsive preview. The HTML tab's Desktop / iPad / Mobile buttons resize the WKWebView frame and swap the User-Agent (iOS Mail / iPad Mail), so @media (max-width: …) rules and any UA-gated CSS branch the way they would on a real phone.
• Inbox sidebar designed for glanceability: two-line rows with the From address (strong, ellipsis) and Subject (dim, ellipsis), relative timestamps ("now / 2m ago / 1h ago / 3d ago") right-aligned, attachment marker (📎N) on row 2 when applicable. Hover lifts to a soft accent bar; selection gets the full accent left edge.
• Theme built around an explicit four-step surface hierarchy (BG → BG_ELEV → BG_ELEV2 → BG_SOFT) with helper functions for body/muted/dim text and surface levels. Settings dialog uses heading-with-underline sections (no nested cards), primary buttons fill with the brand accent, focus rings are clean 1px borders.
• Native menus and shortcuts: ⌘, Preferences · ⌘Q Quit · j / k / ↓ / ↑ next / prev message · g / G newest / oldest · / focus search · 1-6 switch detail tab · p pause / resume · d delete · ⇧⌘X clear all · t toggle theme · ? shortcuts cheat sheet · Esc close dialog / blur search.
• Detail tabs: HTML (rendered) · Text · Headers (sortable) · Attachments (Save…) · Source (RFC 822 with syntax highlighting) · Release (resend any captured message to a target SMTP URL).
• Hand-drawn icon that pops on the macOS dock; source SVG in icon/icon.svg, baked into AppIcon.icns via make icon.
• scripts/simulate.py ships ~30 ready-to-fire scenarios across work tooling (Linear, GitHub, Figma, Google Docs, Slack-shaped notifications), transactional (Stripe payment, Apple App Store receipt, Google Calendar reminder), newsletters (Substack), and ecommerce (a fictional bikini brand "MARÉ" with six perfectly-curated responsive templates: welcome, drop, order, cart, sale, lookbook). Default firing order is interleaved to look like a plausible day's inbox. Stdlib-only Python; no pip install needed.

#What's removed

• No CLI binary, no --flags — every option is a Preferences field. mailbox-ultra is the .app's executable, not something you run from a terminal.
• No web UI, no HTTP API, no SSE stream. The axum/tower/rust-embed stack is gone. Anything that scraped /api/messages or watched the /events SSE stream needs to switch to the NDJSON log file — same data, line-buffered, tail-friendly.
• No more --update self-update. Updates come from the GitHub releases page; download the new .dmg, drag the new .app into /Applications.
• macOS only. Linux and Windows builds are not produced. WKWebView is macOS-only and we don't want a degraded preview on other platforms.

#Migrating from 0.x

The SMTP port stays at 1025 by default, so anything pointing at 127.0.0.1:1025 keeps working without changes. Old --flag workflows map to Preferences fields one-to-one; open ⌘,, set the field, click Apply. If you were piping --json (NDJSON to stdout) into a tail, switch to Preferences → Logging and tick "Append every captured message as NDJSON to a log file" — same schema.