Mozilla Thunderbird

Mozilla Thunderbird is a free, open-source desktop client for email, calendars and contacts. It is useful for people managing several accounts, local mail archives or a customizable desktop workflow. This cask installs Thunderbird Desktop's Release channel for Mac; it is not the separate ESR cask or an email-hosting subscription.

Features

• Manage multiple email accounts with folders, unified views, search and quick filters.
• Read and compose messages in tabs, organize mail with filters and handle attachments.
• Use local folders and offline copies when configured for the account.
• Manage calendars, tasks and address books, including compatible CalDAV/CardDAV services.
• Use supported IMAP/POP mail retrieval and SMTP sending, and supported Exchange accounts.
• Configure OpenPGP signing/encryption and compatible S/MIME workflows.
• Customize layout and extend functionality with compatible add-ons.

Install and configure

Install with brew install --cask thunderbird, or download the official Mac DMG and move Thunderbird.app into Applications. Open Account Hub and add an existing email account. Verify the provider's server settings, authentication method and required permissions. Test both sending and receiving before importing a large archive or changing the default mail application.

This cask explicitly conflicts with thunderbird@esr; choose the intended channel rather than installing both through those casks. It lists no additional formula dependency. Thunderbird Release brings new features on a roughly monthly schedule; ESR is an annual extended-support branch with maintenance updates. Version numbers and release notes from the two channels are not interchangeable. Back up the profile before major upgrades or changing channels; older software may not safely open a profile updated by a newer version. Check add-on compatibility as well.

Accounts, OAuth and permissions

Thunderbird is a client, not a free mailbox provider. You need an existing email account or a separate hosting service to exchange mail. Your provider controls storage quotas, server access, prices, authentication and organization policies. Some providers require OAuth2, app passwords or administrator consent rather than a normal password. Review the provider's consent screen and requested scopes; Thunderbird must receive appropriate access to read/send mail and synchronize selected services. An organization may restrict third-party clients or Exchange access.

OAuth authorization is different from buying Thunderbird or creating a universal Thunderbird login. Tokens and remembered credentials are retained in the desktop profile; revoke provider access and remove stored tokens when retiring an account. A Primary Password protects remembered credentials, not a guarantee that all local mail is encrypted. Protect your Mac account and profile backups. Grant macOS folder access only where needed for attachments, imports or exports; notifications can be configured independently.

Privacy, security and offline use

Offline availability depends on which messages and attachments have been downloaded. IMAP deletion and moves may synchronize back to the server; local folders and backups are different from server folders. Confirm sync and retention settings before removing mail or accounts, and preserve copies of important messages.

Remote images and other content can reveal activity to senders when loaded. Review remote-content exceptions, cookies, phishing warnings and technical-data settings. OpenPGP requires correctly managed keys and recipient compatibility; it does not make every message automatically encrypted. Keep private keys and recovery material safe and retain profile backups. Add-ons can access sensitive mail or account information according to their permissions, so review them carefully. The free client does not require sending mail through a Thunderbird-operated server, but normal mail/calendar providers and optional online services still receive the data needed for their services.

Mac support and resources

The official 157.0.1 requirements list macOS 10.15 or later, Intel x86 or Apple Silicon, 512 MB RAM and 200 MB application disk space, plus additional space for mail. Treat these published baseline figures separately from practical needs for large accounts, local indexes, attachments and backups. Windows and Linux builds have separate requirements; Linux GTK/glibc packages are not Mac cask dependencies. Thunderbird Mobile for Android is a separate application.

The official English-US 157.0.1 Mac DMG is 158,973,361 bytes, verified by HTTP metadata without downloading the installer. Installed usage and profile size differ from the download. Connectivity is needed to retrieve/send new mail and synchronize remote services; previously downloaded content can be read offline according to settings.

Cost and license

Thunderbird Desktop is free software primarily under Mozilla Public License 2.0, with applicable licenses for included components. No purchase or donation is required to download or use it. Donations are optional. Email hosting, provider subscriptions, paid add-ons and optional Thundermail/Thunderbird Pro services can have separate charges and terms; those are not bundled free accounts or a requirement for ordinary client use.

Sources: Thunderbird Desktop, System requirements, Release channels, Privacy notice, Privacy settings, About and licensing.