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SIEVER Mail

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What SIEVER Mail is

SIEVER Mail is a free, open-source desktop email client built with Electron for Linux, macOS, and Windows. It combines multiple IMAP/SMTP accounts and Gmail OAuth accounts in a unified inbox. Messages can be sorted by date, sender, subject, or size, grouped, filtered for unread or flagged status, and searched with sender, recipient, or subject fields. The interface can place folders, the message list, and the reader beside each other, or use a dense table above the reader. It supports replies, forwards, signatures, attachments, bulk actions, keyboard navigation, and light or dark themes. Mail is stored in a local SQLite database, while credentials use the operating system keychain through Electron safeStorage. The project states that it has no telemetry or third-party tracking. Incoming HTML is sanitized in sandboxed frames, attachments do not execute on click, and IMAP uses SSL/TLS or required STARTTLS. Gmail uses OAuth 2.0 over IMAP/SMTP. It is licensed under Apache 2.0.

Who it suits

SIEVER Mail suits desktop users who manage several IMAP or Gmail accounts and want a unified inbox. It is intended for people comfortable with an actively developing open-source project.

What it does well

  • Supports multiple IMAP/SMTP accounts
  • Unified inbox for supported accounts
  • Local SQLite mail storage
  • No telemetry or third-party tracking
  • Linux, macOS, and Windows support

What to know first

  • No paid plans or trial listed
  • Project remains in active development
  • One build-time extension limit
  • No web or mobile client listed

Verdict

SIEVER Mail focuses on multi-account desktop email with local storage, search, organization, and privacy-oriented handling. Its active-development status and build-time extension model may matter to users seeking a settled platform.

Facts from SIEVER Mail's own pages

Accounts
It supports multiple IMAP/SMTP and Gmail OAuth accounts alongside a unified inbox. · github.com, 12 Oct 2026
App coverage
desktop · github.com, 20 Sept 2026
Attachments
Users can open or save attachments, attach recently used files, and drag files into the composer. · github.com, 12 Oct 2026
Availability
The project is released under the Apache License 2.0. · github.com, 12 Oct 2026
Connections
IMAP connections use SSL/TLS or required STARTTLS, and Gmail access uses OAuth 2.0 over IMAP/SMTP rather than the Gmail HTTP API. · github.com, 12 Oct 2026
Development status
The README describes the application as in active development and says its data layout may change while the 1.x baseline settles. · github.com, 12 Oct 2026
Email support
It supports multiple IMAP/SMTP accounts and Gmail OAuth accounts in the same client. · github.com, 12 Oct 2026
Extensions
A custom fork can attach one extension at build time, with hooks for toolbar actions, settings tabs, dialogs, IPC, and composer fonts and colors. · github.com, 12 Oct 2026
Intended users
The maker describes it as originating with a small engineering team seeking a fast, focused client for multiple accounts and folders. · github.com, 12 Oct 2026
Layouts
It offers side-by-side folders, message list, and reader panes, or a dense table above the reader. · github.com, 12 Oct 2026
License and cost
The public project is released under the Apache License 2.0, and the opened project pages list no paid plans or trial. · github.com, 12 Oct 2026
Local data
Mail data is stored in a local SQLite database, and credentials are handled through the operating system keychain using Electron safeStorage. · github.com, 12 Oct 2026
Mail composition
The composer supports signatures, replies and forwards, and aims to preserve message layout across email clients. · github.com, 12 Oct 2026
Mail workflow
Users can sort and group messages, filter unread or flagged mail, search by sender, recipient or subject, and act on selected messages in bulk. · github.com, 12 Oct 2026
Maintainer and support
The repository says it is authored and maintained by Mattia Beltrami and welcomes issues through its GitHub tracker. · github.com, 12 Oct 2026
Message handling
The client supports replies, forwards, attachments, signatures, bulk actions, keyboard navigation, and light or dark themes. · github.com, 12 Oct 2026
Organization
Users can sort by date, sender, subject, or size; group messages; filter unread or flagged mail; and search with field-specific terms. · github.com, 12 Oct 2026
Platforms
The build documentation lists macOS arm64 and x64, Windows x64, and Linux x64 and arm64 targets. · github.com, 12 Oct 2026
Privacy
The project states that it has no telemetry or third-party tracking. · github.com, 12 Oct 2026
Product
SIEVER Mail is an open-source desktop email client built with Electron. · github.com, 12 Oct 2026
Security
The technical documentation says incoming HTML is sanitized and shown in sandboxed frames, and opened attachments do not execute. · github.com, 12 Oct 2026
Support
The README directs users to the GitHub issue tracker for issues. · github.com, 12 Oct 2026
Unified inbox
Its unified inbox gathers selected accounts’ inboxes and labels each message with its account. · github.com, 12 Oct 2026

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