Curo

The brand

Curo's promise is calm. The brand had to feel like a trusted operator, not another noisy productivity app — so the identity is editorial and quiet: a deep near-black canvas, a single warm-gold accent, and a refined serif display ("Your inbox, handled.") that reads more like a private members' club than a SaaS tool. The voice is reassuring and precise. The recurring visual motif is the triage card — CRITICAL / IMPORTANT / FYI — which doubles as the product's core mental model and the brand's signature.

The frontend

• A live triage console, not a marketing facade — real inbox, real priority rules, drafts rendered inline.
• A teaching loop UI — every correction the user makes ("this is actually important") trains their personal priority model, visibly.
• The Voice Personality engine — Curo profiles how each person writes and renders it as a shareable, sports-card-style "OVR" card (3D flip, OG-unfurl preview, a /vs comparison, and a constellation view) — a genuine virality surface baked into the product.
• A native calendar with a full booking system — public /book/<slug> pages with real availability pulled straight from the user's own calendar, timezone-aware, dual .ics invites sent automatically.
• Multi-account external sync — Google, Microsoft, and CalDAV calendars connect and two-way sync per account, Outlook-style, not just read-only.
• A full theme system (13 light-mode twins of the dark UI) with persistent per-user preference, plus a PWA + native-app shell so it installs like a real app.
• File attachments on every surface — compose, reply, forward — with drag-and-drop staging, not a bolted-on afterthought.

The backend — the serious part

• Multi-tenant architecture — isolated per-account data, served by a FastAPI/uvicorn service under PM2 behind an nginx + Cloudflare edge.
• Zero-knowledge mailbox encryption — every connected mailbox's credentials are encrypted at rest with a Fernet key; the platform stores nothing it could leak in the clear.
• Universal mailbox ingestion — IMAP/SMTP connectors unify Gmail, Outlook, and any provider into one secure plane; a single account linked 16 real mailboxes at once.
• A provider-agnostic AI triage engine — pluggable across Anthropic and DeepSeek, with a PriorityRule teaching loop that learns each user's definition of "important."
• The voice engine — signature/contact-scrubbing, reactive tone-shifts, and per-relationship discourse modelling so drafts sound like you, to that person.
• Metered AI billing and spend-gating so cost never runs away — every model call is budgeted and tracked.
• Prompt-injection defense — a purpose-built exfiltration-defense layer: output filtering and verification on every AI-touched surface, a real CSP, a same-origin image proxy that decodes and re-encodes every remote image, and an evidence table logging every detected injection attempt.
• Native push notifications (FCM) and a two-way calendar sync engine across every connected provider — not a one-time import, a living connection.
• Server-side A/B testing infrastructure — sticky variant assignment, impression + conversion tracking, all measured, not guessed.

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