On-device summaries
Message and conversation summaries run entirely on your Mac; nothing is sent to a server. Apple Intelligence handles them out of the box, and an optional local model pack takes over once installed, with the biggest gains on long threads.
What still uses the network
The usual things: syncing your mail, signing in, and fetching attachments you haven't opened before. Beyond those, the full list:
- Update checks — the app periodically checks kestrelmail.app for signed updates.
- Account setup — Kestrel may look up your provider's server settings, including through Mozilla's public autoconfig directory, which sees only your email domain.
- Unsubscribe — clicking Unsubscribe sends the request to the sender's unsubscribe service.
- Remote images — off by default; if you enable them, images load directly from the sender's servers.
- Model pack — a single download from our server, if you choose to install it.
None of these send your email content to us or to any AI service.
Local caching
Kestrel caches messages and attachments on your Mac, so most of the time it doesn't need to contact the server at all. That means faster reads and less of your data in transit. Drafts save locally first too, then sync in the background. Actions like archive or delete get queued and replayed when you're back online.
Tracker protection
Kestrel blocks known email trackers by default before they load. Remote images from tracking domains, tracking pixels, and hidden resources embedded in message HTML are stripped before you see the message, using a blocklist of several thousand known tracking domains that ships with the app. Remote images are also off by default, which catches trackers no list knows about. Both settings are in Settings > Privacy.
Secure storage
Account passwords and tokens are stored in the macOS Keychain. Drafts, queued actions, and account settings are encrypted on disk with keys held in the Keychain. Cached messages and attachments are stored in a local database that stays on your Mac; enable FileVault to protect it at rest.
Encrypted connections only
All connections to mail servers use TLS — the app won't connect over plaintext. Message content is also cleaned up before it's displayed, so hidden scripts and malicious links embedded in emails can't run on your Mac.
No telemetry
There's no analytics, no crash reporting, and no usage tracking. Nothing about how you use the app is collected or sent anywhere, and every connection the app makes is listed above.
Optional enhanced model pack
Once installed, the enhanced model pack handles all summary generation, with the biggest improvement on long, multi-sender threads. Like everything else, it runs entirely on your Mac. Installing it is your choice, and the app always shows whether it's installed, downloading, or removed.
This may evolve
Kestrel Mail is in active development and some details may change before launch. The direction won't: keep your data local, be transparent about what uses the network, and never sell or share your information.