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mailbox alternatives · Email

Open-source alternatives to mailbox

mailbox 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.

mailbox is a paid product with a free trial, starting at €1 per month, annual payment only (€12 a year, Light). 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 mailbox

  1. Posteo

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

    • Posteo starts at €1 per month, prepaid (minimum top-up €12). mailbox starts at €1 per month, annual payment only (€12 a year, Light).
    • Posteo is open source, according to its own site.
    • Posteo also covers notes.
    • mailbox also covers tasks, documents, video calls and file sync.
    Posteo vs mailboxPosteo 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). mailbox starts at €1 per month, annual payment only (€12 a year, Light).
    • Tuta Mail has a free plan. mailbox does not, though it has a free trial.
    • Only Tuta Mail lists Windows, macOS, Linux, iOS and Android apps.
    • Tuta Mail is open source, according to its own site.
    Tuta Mail vs mailboxTuta Mail pricing and details

  3. 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. mailbox starts at €1 per month, annual payment only (€12 a year, Light).
    • Proton Mail has a free plan. mailbox does not, though it has a free trial.
    • Only Proton Mail lists macOS, Windows, Linux, iOS and Android apps.
    • Proton Mail is open source, according to its own site.
    Proton Mail vs mailboxProton Mail pricing and details

  4. Thunderbird

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

    • Thunderbird is free. mailbox starts at €1 per month, annual payment only (€12 a year, Light).
    • Thunderbird has a free plan. mailbox does not, though it has a free trial.
    • Only Thunderbird lists Windows, macOS, Linux and Android apps.
    • Only mailbox lists a web app.
    Thunderbird pricing and details

  5. Wino Mail

    Free, open source mail and calendar app for Windows

    • Wino Mail has a free plan. mailbox does not, though it has a free trial.
    • Only Wino Mail lists a Windows app.
    • Only mailbox lists a web app.
    • Wino Mail is open source, according to its own site.
    Wino Mail 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). mailbox starts at €1 per month, annual payment only (€12 a year, Light).
    • FairEmail has a free plan. mailbox does not, though it has a free trial.
    • Only FairEmail lists an Android app.
    • Only mailbox lists a web app.
    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). mailbox starts at €1 per month, annual payment only (€12 a year, Light).
    • Mailspring has a free plan. mailbox does not, though it has a free trial.
    • Only Mailspring lists macOS, Windows and Linux apps.
    • Only mailbox lists a web app.
    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). mailbox starts at €1 per month, annual payment only (€12 a year, Light).
    • Only Inbox Zero lists macOS, Windows, iOS and Android apps.
    • Only Inbox Zero lists a browser extension.
    • 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 mailbox?

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

Is mailbox open source?

mailbox is not described as open source on its own site. The listing was checked on Oct 6, 2026 against the pages it cites.

Which of these email apps are free?

Tuta Mail, Proton Mail, Thunderbird, Wino Mail, 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 mailbox: the alternatives its listing names first, then the tools that share the most features with it.