The research shortlist
Page updated
ThunderbirdTop pick
Open email, calendar, and contacts for Mac
Metadata checked Aug 18, 2026
Rank 1 for long-term maintenance, community trust, breadth of core features, and straightforward free Mac installation.
The strongest all-round replacement: Thunderbird combines multiple accounts, unified inboxes, search, filtering, calendar, contacts, tasks, and add-ons in a free, community-backed desktop client. It is less Spark-like visually and does not directly reproduce Spark’s AI and collaborative drafting workflow.
- 01Multiple accounts with unified inbox
- 02Search, filtering, tagging, and add-ons
- 03Built-in calendar, contacts, and tasks
- 04Cross-platform desktop support with official macOS downloads
- 05Free, ad-free, open-source distribution
- The interface and workflow are more traditional than Spark; Spark-specific AI and team-collaboration features are not direct built-ins.
- Building from source requires the Mozilla platform checkout as well as the Thunderbird repository.
Evidence sources (13)
- Official Thunderbird desktop repositorySource available ·
- Thunderbird About Your Rights and MPL termsLicense ·
- Thunderbird project overviewWebsite ↗ ·
- Thunderbird Desktop macOS downloadDocumented macOS path ·
- Official Thunderbird release downloadsFree at review time ·
- Thunderbird release notesRelease ·
- Thunderbird calendar product screenshotScreenshots ·
- GitHub REST repository APISource available ·
- Mozilla source LICENSE fileLicense ·
- Thunderbird licensing termsLicense ·
- Official Mac installation instructionsDocumented macOS path ·
- Official release historyRelease ·
- Thunderbird free-forever download and product pageFree at review time ·
Mailspring
Modern unified-inbox email with a free core
Metadata checked Aug 18, 2026
Rank 2 for Spark-like usability, current releases, and polished Mac support, discounted for the smaller ecosystem and Pro-only advanced features.
Full review — capabilities, 2 caveats, evidence
Mailspring is the closest visual and workflow match to Spark among these options, with a unified inbox, fast cross-account search, themes, spell and grammar tools, undo send, and native macOS behavior. Its GPL-licensed core is free, while several advanced productivity and tracking features are sold as Pro extras.
- 01Unified inbox for IMAP and Office 365 accounts
- 02Fast cross-account and Gmail-style search
- 03Undo send, spell checking, and grammar checking
- 04Themes, dark mode, and macOS notifications
- 05Optional Pro features for snooze, tracking, analytics, and read receipts
- Read receipts, link tracking, analytics, contact profiles, and unrestricted snooze/send-later require Mailspring Pro.
- The official homepage says MIT while the repository LICENSE.md and GitHub metadata identify GPL-3.0; resolve that inconsistency before redistribution.
Evidence sources (11)
- Official Mailspring repositorySource available ·
- Mailspring GPL-3.0 license fileLicense ·
- Mailspring releases, latest 1.23.0Release ·
- Mailspring free core and Pro overviewWebsite ↗ ·
- Mailspring Intel and Apple Silicon Mac downloadsDocumented macOS path ·
- Mailspring signatures product screenshotScreenshots ·
- Mailspring tracking product screenshotScreenshots ·
- GitHub REST repository APISource available ·
- GitHub license metadataLicense ·
- Latest GitHub releaseRelease ·
- Project homepageWebsite ↗ ·
Betterbird
A power-user Thunderbird fork with current Mac builds
Metadata checked Aug 18, 2026
Rank 3 for its active Thunderbird-based development and useful power-user improvements, with deductions for project scale and Mac packaging friction.
Full review — capabilities, 3 caveats, evidence
Betterbird follows Thunderbird ESR and adds targeted bug fixes and workflow controls such as multi-line view, account colors, attachments on top, complex and regular-expression search, and encrypted-message search. It is a capable free option for Thunderbird users, but the project and Mac distribution are less polished and less broadly trusted.
- 01Thunderbird-compatible email, calendar, and contacts stack
- 02Multi-line view and configurable account colors
- 03Attachments-on-top and recent-file attachment support
- 04Complex, regular-expression, and encrypted-message search
- 05Intel and Apple Silicon Mac disk images
- Mac builds are not notarized, so Gatekeeper may require the documented manual workaround.
- The 153 series is explicitly a preview; the current stable download is 140.13.0esr-bb25.
- The official GitHub repository publishes Betterbird patches and build scripts; the underlying Thunderbird source remains in Mozilla repositories.
Evidence sources (14)
- Official Betterbird patches repositorySource available ·
- Betterbird MPL-2.0 license fileLicense ·
- Betterbird project homepageWebsite ↗ ·
- Betterbird macOS system requirementsDocumented macOS path ·
- Betterbird current free downloads and Mac DMGsFree at review time ·
- Betterbird release notesRelease ·
- Betterbird project iconScreenshots ·
- Betterbird product comparison screenshotScreenshots ·
- GitHub REST repository APISource available ·
- GitHub default branch statusSource available ·
- Current Betterbird macOS x86 release downloadFree at review time ·
- Betterbird multi-line view screenshotScreenshots ·
- Betterbird system tray screenshotScreenshots ·
- Betterbird recent-file attachment screenshotScreenshots ·
Specifications, side by side
| Attribute | 1 · Thunderbird | 2 · Mailspring | 3 · Betterbird |
|---|---|---|---|
| License | MPL-2.0 | GPL-3.0-only | MPL-2.0 |
| Platforms | macOS, Windows, Linux | macOS, Windows, Linux | macOS, Windows, Linux |
| Status | Checked | Checked | Checked |
| Version | — | v1.23.0 | v140.13.0esr-bb25 |
| Stars | 111 | 17.7k | 957 |
| Last push | |||
| Caveats | 2 | 2 | 3 |
About Spark Mail
Spark — AI-powered email client for Mac. Manage multiple inboxes and calendars, highlight important messages, summarize and draft emails with AI, collaborate with your team, and integrate with your favorite apps for a smoother workflow.
Setapp listing: Manage emails easier
