S² Mail is built from a long product questionnaire, not a feature dump. The default is Gmail-simple. The power is there when you ask for it. The mail never has to transit our cloud.
Accounts
Your accounts, your servers
S² Mail is a mail client, not a new inbox in the cloud. Add Gmail, Microsoft 365, IMAP, or JMAP. No S² account is required to read or send.
Works with the addresses you already have
OAuth for Google and Microsoft, plus IMAP/SMTP when you need it
Capability-aware UI — we never fake a feature the server does not support
Each account syncs and recovers on its own so one failure cannot take down the rest
Inbox
Simple by default, powerful when asked
The first screen should feel familiar. Power User Mode, extra panels, and diagnostics stay out of the way until you want them.
Gmail-like default layout with an optional reading pane
Classic Inbox is the starting default — Smart Inbox is optional, never forced
Workspaces group accounts, layouts, and identities
Tabs, split views, and native windowing on the desktop
Conversations
Smart Threads
Threads are reconstructed from internet mail standards, then improved with provider-native IDs when they are available.
Message-ID, In-Reply-To, References, subject, and participants
Multi-account conversations stay together in a workspace
Reply uses the correct sending identity
No lock-in to a single vendor’s threading model
Find anything
Local search and Ctrl+K
Search is a local engine. It works without a network and without AI. The Command Center is the keyboard front door to the whole app.
Full-text search across your local mail
Structured filters and thread-aware results
Ctrl+K / Cmd+K command palette
Configurable shortcuts with Gmail- and Outlook-inspired presets
Write and send
Composer, drafts, and a real outbox
Sending is transactional. A message is snapshotted, queued, and reconciled with the server — including when you are offline.
Local-first drafts with autosave and crash recovery
Durable outbox with retry and duplicate protection
Undo send and scheduled send
Correct MIME output, identities, and Sent-folder sync
Stay in control
Offline, rules, snooze, follow-up
Offline is not a special mode. Locally valid work continues, then syncs when the network returns.
Read, search, draft, and queue sends without connectivity
Local mail rules and automation
Snooze threads until later
Awaiting-reply follow-ups and a desktop notification center
Desktop
Built as a native desktop app
Windows, macOS, and Linux. S² Mail registers as a mail client, opens .eml files, and stays out of the way in the tray.
Windows installer and portable build
macOS for Apple silicon and Intel
Linux AppImage and .deb
mailto:, default mail client, and signed updates that never see your mail
