Marco, a privacy-first, offline-first email client (IMAP-native, no AI)

Hey HN. I'm Isaac, and I'm building Marco (https://marcoapp.io), a cross-platform email client that works with any IMAP provider. macOS, iOS, and web today.I started Marco because I finally lost patience with Apple Mail, and the email client market has a weird gap. Legacy clients look terrible and/or are not cross-platform. The good ones scan your data or cost $300+/year. And there's a graveyard of startups (Tempo, Big Mail, Caley) who built beautiful products and shut down after a year or two.I made a few opinionated bets early on:1. IMAP-first, not Gmail API-first. Nearly every email startup builds on the Gmail API. It's convenient, but it locks you into one provider. Marco is IMAP-native, which means it works with Gmail, Outlook, iCloud, Fastmail, custom domains, and any provider that supports IMAP.2. Offline-first. You should be able to read, reply, delete, and organise email on a plane with no wifi. When you reconnect, everything syncs. This requirement nearly killed me. I went through WatermelonDB, Triplit, InstantDB, PowerSync, and Replicache before landing on my current approach: regular HTTP endpoints with TanStack DB and TanStack Query, using IndexedDB on web and SQLite on mobile as storage layers. I ditched "fully fledged" sync engines entirely. Turns out, for my data volumes (hundreds of thousands of entities per user), every sync engine I tried either choked on performance or added complexity I didn't need. I wrote about this journey in detail: https://marcoapp.io/blog/offline-first-landscape3. No AI. This is intentional. Every email client launching right now leads with AI. I think most of it is noise that none of us want or need. Marco is a tool. It should be fast, reliable, and stay out of your way. No email summarisation, no smart replies, no "AI powered" anything.The stack is React Native with Expo, Node.js backend on Railway, Postgres, Redis, S3, etc (all privately networked). Yes, a lightweight backend is needed to facilitate things like push notifications. One codebase across all frontend platforms, 100% shared code.Marco is bootstrapped and profitable at $8/month with a 7-day free trial. 2,000+ users, all organic. No VC, no paid marketing.Would love feedback from HN. Happy to go deep on IMAP internals, the offline-first landscape, or any of the technical decisions.