Spark alternative
Spark checks for new mail
every 60 seconds.
Spark Premium is $8 a month, and your mail passes through Readdle's servers to power its features. Synapse uses IMAP IDLE and the native Gmail API: new messages appear the moment your provider has them. One payment, €4.99, done.
No account required · Payment via Gumroad
The 5-year cost
Synapse
€4.99
Total. Forever.
Spark Premium
$480
$7.99/mo × 60 months
IDLE push vs polling
Most email clients, including Spark on Windows, check for new mail on a timer. Every 60 seconds, they ask your mail server "anything new?" That's polling. IMAP IDLE is different: the server notifies the client the moment a message arrives. Synapse uses IDLE for IMAP accounts and the native Gmail push API for Google accounts. You see new mail the second it lands, not the next time the timer fires.
Your mail stays off Readdle's servers
Spark's shared inboxes, AI features, and smart notifications are powered by Readdle's cloud infrastructure, which means your email passes through their servers. Synapse has no cloud of its own. Mail syncs directly from your provider (Gmail, Outlook, or any IMAP server) to a local SQLite database on your machine. Nothing in between.
AI that runs offline
Spark's AI features process your email content remotely. Synapse runs Qwen3.5-4B on your GPU via Vulkan. Reply suggestions, summaries, and plugin actions are generated locally: 0 bytes sent to any AI API. Enable it from Settings → AI with a one-time ~2.5 GB download and it works without an internet connection from that point on.
One payment and you're done
Spark Premium renews every month. Cancel and the advanced features disappear. Synapse is €4.99 once, and that includes every future update. If I stop shipping, the app keeps working. Your data is local, there's no server dependency that can expire.
Lifetime access · All future updates included
Email done right
- Gmail REST API + IMAP IDLE push for all other providers, no polling
- Thread view with expandable conversations and newest-first toggle
- Bulk actions: move, delete, archive, mark read with keyboard support
- One-click unsubscribe from any mailing list
- Open .eml attachments inline without leaving your inbox
- Italian PEC certified email (S/MIME auto-extracted)
- OAuth2 for Google and Microsoft, password never stored
Search that actually works
- Gmail-style query DSL: from:, subject:, is:unread, has:attachment and more
- BM25 full-text + 768-dim multilingual semantic search, 100+ languages
- Smart reranker: keyword score, semantic similarity, recency, personal history
- Search inside attachments and nested .eml files
- Saved searches, history, and contact autocomplete typeahead
AI without the cloud
- On-device AI assistant (Qwen3.5-4B, Vulkan GPU)
- Local model: 0 bytes to OpenAI. Or BYOK your own key.
- Grammar-constrained plugin output: structured JSON, no hallucinated fields
- Auto low-memory mode on machines with 16 GB RAM or less
Privacy you can verify
- TPM-sealed AES-256 credential vault
- Offline-first SQLite, all data stays on your machine
- 0 telemetry, 0 analytics, 0 cloud relay
What else you get
- Asana · ClickUp · Calendar · Reminders plugins
- 28 themes across light, dark, half-dark, and aurora variants
- Gmail-style and Mailbird-style keyboard shortcut presets
- Multi-language spellcheck in compose
- Built-in address book
- Automatic Ed25519-signed updates, no manual downloads