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Fastmail alternatives · Email

Open-source alternatives to Fastmail

Fastmail is not described as open source on its own site. 8 of the 51 other email apps in this directory are open source, according to their own sites.

Fastmail is a paid product with a free trial, starting at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly. 6 of them are free or have a free plan.

8 tools · Listings checked up to Oct 9, 2026 · Where the facts come from

How each one differs from Fastmail

  1. Proton Mail

    End-to-end encrypted email service based in Switzerland

    • Proton Mail starts at $3.99 per month, billed every 12 months ($47.88); $4.99 billed monthly. Fastmail starts at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly.
    • Proton Mail has a free plan. Fastmail does not, though it has a free trial.
    • Proton Mail is open source and end-to-end encrypted, according to its own site.
    Proton Mail vs FastmailProton Mail pricing and details

  2. Tuta Mail

    End-to-end encrypted email and calendar from Germany

    • Tuta Mail starts at €3 per month, paid yearly (lowest paid personal plan). Fastmail starts at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly.
    • Tuta Mail has a free plan. Fastmail does not, though it has a free trial.
    • Tuta Mail is open source and end-to-end encrypted, according to its own site.
    Tuta Mail vs FastmailTuta Mail pricing and details

  3. Wino Mail

    Free, open source mail and calendar app for Windows

    • Wino Mail has a free plan. Fastmail does not, though it has a free trial.
    • Only Fastmail lists a web app.
    • Only Fastmail lists macOS, Linux, iOS and Android apps.
    • Wino Mail is open source, according to its own site.
    Wino Mail pricing and details

  4. Thunderbird

    Free, open-source email app for Windows, macOS, Linux and Android

    • Thunderbird is free. Fastmail starts at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly.
    • Thunderbird has a free plan. Fastmail does not, though it has a free trial.
    • Only Fastmail lists a web app.
    • Only Fastmail lists an iOS app.
    Thunderbird pricing and details

  5. Posteo

    Ad-free, green-powered email from Berlin for €1 a month

    • Posteo starts at €1 per month, prepaid (minimum top-up €12). Fastmail starts at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly.
    • Only Fastmail lists Windows, macOS, Linux, iOS and Android apps.
    • Posteo is open source and end-to-end encrypted, according to its own site.
    • Posteo also covers notes.
    Posteo pricing and details

  6. FairEmail

    Open source, privacy-oriented email client for Android

    • FairEmail starts at $7.49 one-time (pro features, US Google Play in-app purchase). Fastmail starts at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly.
    • FairEmail has a free plan. Fastmail does not, though it has a free trial.
    • Only Fastmail lists a web app.
    • Only Fastmail lists Windows, macOS, Linux and iOS apps.
    FairEmail pricing and details

  7. Mailspring

    Open-source desktop email client for Mac, Windows and Linux

    • Mailspring starts at $8 per month, or $85 per year (Mailspring Pro). Fastmail starts at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly.
    • Mailspring has a free plan. Fastmail does not, though it has a free trial.
    • Only Fastmail lists a web app.
    • Only Fastmail lists iOS and Android apps.
    Mailspring pricing and details

  8. Inbox Zero

    Open source AI email assistant for Gmail and Outlook

    • Inbox Zero starts at $18 per user / month, billed annually ($20 billed monthly). Fastmail starts at $3 per user / month, billed yearly (Basic); Individual is $5, billed yearly.
    • Only Inbox Zero lists a browser extension.
    • Only Fastmail lists a Linux app.
    • Inbox Zero is open source and self-hostable, according to its own site.
    Inbox Zero pricing and details

Common questions

Is there an open-source alternative to Fastmail?

Yes. Proton Mail, Tuta Mail, Wino Mail, Thunderbird, Posteo, FairEmail, Mailspring and Inbox Zero are open source, according to their own sites.

Is Fastmail open source?

Fastmail is not described as open source on its own site. The listing was checked on Oct 5, 2026 against the pages it cites.

Which of these email apps are free?

Proton Mail, Tuta Mail, Wino Mail, Thunderbird, FairEmail and Mailspring are free or have a free plan.

When was this checked?

Each listing shows its own date. On this page they run from Oct 4, 2026 to Oct 9, 2026. Vendors change prices and plans without notice, so confirm on their site before you buy.

This page is built from the listings. A tool is here because its listing says so, and the order is how close each is to Fastmail: the alternatives its listing names first, then the tools that share the most features with it.