Updated May 1, 2026

Spark is a fine email app. Epistles is for people who would rather their mail not pass through anyone’s server but their provider’s.

Spark Mail, by Readdle, has been a thoughtful multi-account client for years. It is loved, and the affection is earned. The honest comparison is not feature-versus-feature; it is architectural. Spark’s cross-device sync, push notifications, and team collaboration are all powered by Readdle’s servers. Epistles keeps mail on the device-to-provider channel and stores only credentials, in a vault we cannot decrypt.

What Spark does well

Spark is a polished cross-platform client with real depth. The Smart Inbox separates conversations from newsletters without making you build a rule for every sender. Pin, Set Aside, Done, and Mute give you a vocabulary for triage that is more considered than archive-or-trash. Snooze and Send Later are first-class. The mobile apps are excellent.

Team collaboration is the real differentiator. Shared drafts let two people compose a reply together, with private comments visible only to the team. Delegation, shared inboxes, and read statuses sit on top of that. If your work is genuinely collaborative, these features matter, and Epistles does not have them.

Spark also ships AI features through Spark +AI: writing assistance, summarization, translation, and meeting notes. Whether you want AI in your inbox is your call; Spark has built the feature carefully.

Where Spark stops

The architectural difference is the centre of this page. Spark’s own documentation says it plainly: when a message arrives at your provider, Spark’s servers fetch a portion of it (subject and partial body) to push a notification to your devices, then delete that data after roughly four hours. Team features, scheduled sends, and templates rely on encrypted server-side storage at Readdle. Account access tokens are kept on Readdle’s servers as well, which is how a Spark app on a second device reaches your inbox without re-authenticating to Gmail.

None of this is hidden, and the data is encrypted in transit and at rest. The question is not whether Readdle is trustworthy; it is whether you want any third party in the path between your provider and your inbox.

Spark runs on macOS, iOS, Android, Windows, and Apple Watch. There is no Linux app and no native ProtonMail support; ProtonMail works only via Proton’s Bridge over IMAP/SMTP, which needs a desktop running somewhere for the phone app to reach it. Pricing leans into AI and team tiers: Free, Plus at $8.25/month annually, Pro at $16.58/month annually, and a custom Enterprise tier.

What Epistles ships that Spark does not

Local-first storage with a zero-knowledge vault. Mail moves directly between your device and your provider over native protocols. Our infrastructure never sees the body, subject, or recipients of a message. The only thing we hold is a Cloud Vault of account credentials, wrapped on your device with a key derived from your Epistles password and stored as opaque AES-256-GCM ciphertext we cannot decrypt. Sign in on a second device, type your password, and your accounts come back.

Five providers, native protocols. Gmail through the Gmail API, Microsoft 365 through MS Graph, Fastmail through JMAP, ProtonMail through Proton’s API with OpenPGP decryption on device, and any IMAP/SMTP host as the catch-all. ProtonMail works without Bridge, on every platform we ship to.

Linux as a first-class platform. A signed APT, DNF, and Flatpak repos at repo.epistles.com, all from the same Tauri 2 codebase as the Mac app. macOS, Linux, iOS, and Android ship today; Windows and a web app at app.epistles.com are in build with honest "coming" badges.

No telemetry, no analytics, no crash SDKs. The app makes only the network calls it needs: talk to your providers, sync your encrypted credential blob, fetch updates. There is no second channel reporting back what you do inside the client. Diagnostics are on-device logs you can export when you need them.

Open-source intent. The working tree is migrating to github.com/epistlesapp/epistles; when that lands, every claim on this page maps to code you can read.

Pricing without tiers. Three accounts on Free. Pro is $35 a year, with a fifteen-day trial that asks for no card. There is no Plus, no Pro+, no Enterprise.

Where Spark wins

Spark’s team-collaboration features are real, well-designed, and not on our 2026 roadmap. If two or more people need to co-author replies, comment privately, share an inbox, or delegate triage, Spark is the right pick. We do not have a meaningful answer to that workflow.

Spark is also more mature on the productivity surface. It ships Snooze, Send Later, and Schedule Send today; we are still building those, with Snooze waiting on a relay piece we want to design correctly rather than ship as a per-provider patchwork. Spark’s AI density is higher; we have not built AI into the client yet, by choice.

The matrix, plainly

Platforms shipping today: Spark: macOS, iOS, Android, Windows, Apple Watch. Epistles: macOS, Linux, iOS, Android. (Epistles Windows and web in development.)
Email providers supported: Spark: Gmail, Microsoft 365/Outlook, iCloud, Yahoo, Exchange, IMAP. Epistles: Gmail, Microsoft 365, Fastmail (JMAP), ProtonMail (native, no Bridge), IMAP/SMTP.
Storage architecture: Spark: mail body stays at the provider; subject and partial body cached on Readdle servers for push (~4 hours); team-feature data, scheduled sends, and account tokens persisted on Readdle servers. Epistles: mail in local SQLite, protected at rest by the OS disk encryption (FileVault, BitLocker, Data Protection, FBE); nothing about your mail traverses our infrastructure.
Cross-device sync model: Spark: Readdle-server mediated. Epistles: zero-knowledge Cloud Vault; credentials encrypted under your password, stored as opaque ciphertext we cannot decrypt.
Team features: Spark: shared drafts, private comments, delegation, shared inboxes, read statuses. Epistles: none today; not on the 2026 roadmap.
AI features: Spark: writing assistance, summarization, translation, meeting notes (Plus and Pro tiers). Epistles: none in the client.
Pricing: Spark: Free; Plus $8.25/mo annually; Pro $16.58/mo annually; Enterprise on request. Epistles: Free for 3 accounts; Pro $35/yr (15-day trial, no card).
Telemetry: Spark: collects analytics for product improvement, per its privacy policy. Epistles: zero analytics, zero crash-reporting SDKs, zero metrics.
Open source: Spark: closed-source. Epistles: migrating to a public repository at github.com/epistlesapp/epistles.

Who should pick which

If you share an inbox, comment on drafts, or delegate replies, pick Spark. The collaboration depth is real and we do not match it. If you also live in AI-assisted composition and meeting summaries, Spark is further down that road than we are.

If the architectural section gave you pause, that is the signal. Spark holding subject lines and partial bodies briefly for push, and tokens and team-feature state persistently, is not a scandal; it is how the product is built. For some people it is a deal-breaker, and those are the people we built Epistles for.

If you also use Linux, or you want ProtonMail without running Bridge on a desktop, the choice is forced. Spark does not ship to those configurations; Epistles does, today, from the same codebase as the Mac app.

A line at the end

Spark is a careful, mature product, and a lot of people are happy with where Readdle has landed the trade-offs. Epistles draws the line in a different place. If that line is the one you have been looking for, our front door is here.