Kestrel vs Spark
Spark is an email app from Readdle for Mac, Windows, iPhone, iPad and Android, with a free plan and AI on its Plus and Pro plans. It processes most mail on your device, but some features, such as Send Later and shared emails, run on Spark's servers, and its AI uses providers such as OpenAI and Anthropic. Kestrel is a Mac app that syncs straight with Gmail or your IMAP server and runs its AI on your Mac or on your own Anthropic key.
At a glance
| Feature | Kestrel | Spark |
|---|---|---|
| Price | $20 a year, on up to 3 Macs | Free; Plus $99 a year |
| Platforms | Mac | Mac, Windows, iPhone, iPad, Android |
| Mail accounts | Gmail and any IMAP account | Gmail, Outlook, iCloud, Yahoo, Exchange, IMAP |
| Mail passes through | Your provider, and Anthropic if you add a key | Your provider, and Spark's servers for some features |
| AI | On your Mac, or with your own Anthropic key | Plus and Pro, through OpenAI, Anthropic and others |
| Account needed | None, a license key | A Spark account |
Where your mail is handled
Spark processes most mail on your device, but its servers keep recent emails for four hours and hold Send Later emails, shared emails and team data. Its AI features send emails and drafts to providers such as OpenAI and Anthropic.
Kestrel syncs straight between your Mac and Google or your IMAP server. Send Later and reminders run on your Mac, so Kestrel has to be running when one is due; if it isn't, it catches up the next time you open it. Its AI runs on Apple Intelligence or on your own Anthropic key.
Platforms and price
Spark has a free plan and runs on Mac, Windows, iPhone, iPad and Android, with one subscription for all of them. Kestrel is Mac only and costs $20 a year for up to 3 Macs, with a free demo inbox to try first.
Which one to pick
Pick Kestrel if
- You want Send Later and reminders handled on your Mac, not on a server.
- You want AI that runs on your Mac or on your own Anthropic key.
- You don't want an account with the app's maker.
Pick Spark if
- You want an app on Windows, iPhone, iPad or Android. Kestrel is Mac only.
- You want a free plan.
- You want AI without macOS 26 or an API key of your own.
The details
| Detail | Kestrel | Spark |
|---|---|---|
| Price | $20 a year for a license key, bought on account.laibe.cc. One key works on 3 Macs. The demo inbox, with made-up mail, is free to try. | A free plan with unlimited accounts. Plus is $10 a month or $99 a year and Pro $20 a month or $199 a year, as the US Mac App Store lists them, with a seven-day trial in the app. One subscription works on every device. |
| Platforms | Mac only, on macOS 15 or later. A direct download, not on the Mac App Store, and it updates itself. | Mac (macOS 13 from Spark's site, 12 from the Mac App Store), Windows 10 or later, iPhone and iPad on iOS 16.4 or later, and Android 10 or later. |
| Mail accounts | Gmail and Google Calendar, through a free Google Cloud project you create yourself in about five minutes. Any IMAP account for mail, with Proton Mail (through Proton Mail Bridge), Fastmail and iCloud Mail filled in for you. IMAP accounts have no calendar and keep recent mail only, such as the latest 400 in the inbox. | Gmail, Outlook, Hotmail, Exchange, iCloud, Yahoo, AOL, GMX and any IMAP account, in one unified inbox. |
| Where your mail goes | Straight between your Mac and Google or your IMAP server. Kestrel's own servers see no mail. account.laibe.cc checks the license key, and kestrel.laibe.cc offers updates if you allow it. Sign-ins, mail passwords and API keys stay in the macOS keychain. Read statuses, team comments and booking pages need a team server you deploy to your own Cloudflare account. | Spark says mail is mostly processed on your device. Its servers keep recent emails for four hours, Send Later emails until they are sent, and shared emails, drafts and team data, on servers in the US and the EEA. Sign-ins are stored as tokens. |
| AI | Kestrel AI writes and rewrites drafts, summarizes threads, answers questions about your mail and labels new mail. It runs on Apple Intelligence on your Mac (macOS 26), or on Claude with your own Anthropic API key, which sends the text a feature needs to Anthropic. Auto Labels is on by default, and every part can be turned off. AI apps such as Claude Code can search, triage and draft through its MCP server, never send. | Spark +AI writes, summarizes and translates, and the AI Assistant finds and acts on mail, on Plus and Pro. Free users get a limited preview. Spark uses on-device models and third-party providers such as OpenAI, Azure OpenAI, Anthropic and Google's Vertex AI, which may keep inputs for up to 30 days. Spark says it doesn't train AI on your data. |
| Keyboard | Every action has a key: E marks done, H sets a reminder, # trashes, / searches. ⌘K finds any action or folder by name and shows its key. A practice inbox teaches the first keys. | Shortcut sets from Spark, Apple Mail, Gmail and Superhuman, or a custom set, on Mac and Windows. Spark for Android has no shortcut settings. |
| To sign up | No Kestrel account. You sign in to Google or your IMAP server, and add a license key. | A Spark account, created under the email address you first sign in with. |
Sources
Spark’s side was checked against these pages on . Write to [email protected] if something has changed.