Thunderbird for business, instead of Outlook

Thunderbird replaces Outlook

Thunderbird reads mail over IMAP from any provider, handles calendars over CalDAV and contacts over CardDAV. It runs on Windows, macOS and Linux, with no per-seat licence (MPL 2.0 licence).

Since version 153 ESR, released on 21 July 2026, Thunderbird also connects to Exchange without an add-on, through Exchange Web Services (EWS), for email. Version 154, released on 18 August 2026, added Microsoft Graph for Microsoft 365 accounts. Exchange calendars and contacts are still in development.

Microsoft has blocked EWS by default in Exchange Online since 1 October 2026, except for apps allowed by the administrator, and retires it on 1 April 2027. To keep Thunderbird on Microsoft 365, you therefore need the Release channel, which speaks Graph. With hosted email in Europe, Thunderbird uses IMAP, CalDAV and CardDAV.

Deployment on every computer

• Silent installation with the official MSI package (64-bit Windows), through WAPT, a GPO, SCCM or Intune. On Linux, the distribution package or Flatpak.
• Settings enforced by policies.json: add-ons installed and locked, updates left to the device management tool, telemetry off, shared tags. The same file works on Windows, macOS and Linux. ADMX templates exist for GPOs.
• Preferences locked by AutoConfig (autoconfig.js and a .cfg file) for what policies do not cover, such as per-identity signatures.
• Simpler account creation: users enter their name, address and password, and Thunderbird finds the servers from the domain's configuration file.
• With WAPT, the daily audit restores any configuration file changed on a computer.

{
  "policies": {
    "DisableAppUpdate": true,
    "DisableTelemetry": true,
    "ExtensionUpdate": false,
    "ExtensionSettings": {
      "{8845E3B3-E8FB-40E2-95E9-EC40294818C4}": {
        "installation_mode": "force_installed",
        "install_url": "file:///C:/ProgramData/Thunderbird/extensions/quicktext.xpi"
      }
    },
    "Preferences": {
      "mailnews.tags.devis.tag": { "Value": "Devis", "Status": "locked" },
      "mailnews.tags.devis.color": { "Value": "#550000", "Status": "locked" }
    }
  }
}

Release or ESR

Two ESR versions overlap for about 12 weeks, leaving time to test the next one. As of 13 November 2026, the Release channel is 159 and the ESR is 153.6.

For a fleet that depends on add-ons such as Quicktext, we recommend the ESR, unless computers need to read Microsoft 365 mailboxes.

Migrating from Outlook

1. Inventory of accounts, PST files, mail rules, signatures and Outlook add-ons.
2. Mail kept on the server (IMAP or Exchange): Thunderbird downloads it, no import needed.
3. PST archives: Thunderbird's import tool reads data from an Outlook installed on the same computer. Without Outlook, we convert PST files to mbox with readpst, a free software tool, then import them.
4. Contacts and calendars: vCard and iCalendar export, or CardDAV and CalDAV sync with the mail server or Nextcloud.
5. Signatures, tags and reply templates moved into the central configuration.
6. User training: folders, filters, search, shared calendars, templates.

The steps are detailed in our guide Migrating from Outlook to Thunderbird.