Great questions.

1. It is _both_ local and hosted. The client itself is fully offline-capable, including proper full-text search (single digit ms), writing drafts – anything you would expect an email client to do. The "hosted" bit is to ensure rapid synchronisation across multiple clients (ie your desktop and mobile).

2. Some metadata is hosted in pg to facilitate cross-platform synchronisation, as mentioned. This is encrypted at rest on a provider with SOC 2 Type I certification. Further symmetric encryption (AES-256) of sensitive columns is also done. We're well aware that security is the most important aspect of this product and is our primary focus.

3. We've not forked Thunderbird. Marco has been built from the ground up, both on the FE and BE, and has been a monumental task.

4. We have no immediate plans to add SMS/WhatsApp/RSS. If those interest you, you might have a look at Missive.

We understand that storing email metadata is potentially a turn-off to some, but is actually the key driver to an entirely new email experience. It means that a Marco client itself is virtually stateless (save for some lightweight metadata) and syncs instantly across N number of clients – it runs on web/OSX/Windows/Android/etc, and changes propagate between them instantly. New client setup happens via Marco in a proprietary way on the order of seconds and doesn't take hours to sync via IMAP.

We're building this for ourselves. Thunderbird is "alright". Apple Mail is "alright". Superhuman is decent, but ridiculously expensive and Google/Microsoft only. Missive is fairly decent (and also stores metadata), but is built for team collaboration, not individual use.

> New client setup happens via Marco in a proprietary way on the order of seconds

Do you consider this your "ActiveSync" and if so what do you see as the differentiating features/capabilities?