Thunderbird, the long-standing open-source email client, has announced a major new initiative to expand beyond the desktop with a suite of cloud-based services under the branding “Thunderbird Pro.”
These offerings include a privacy-respecting email service called “Thundermail,” an encrypted file-sharing platform, a scheduling tool, and an optional AI assistant — aiming to provide an open-source alternative to proprietary ecosystems like Gmail and Office365.
The announcement, made by Thunderbird Managing Director of Product Ryan Sipes, represents a strategic pivot for the project, which has historically focused on local, device-based applications. While the core Thunderbird app will remain free and unaffected, the new Pro services mark Thunderbird's first major foray into subscription-based infrastructure, with sustainability and user freedom as guiding principles.
The Why for offering these services is simple. Thunderbird loses users each day to rich ecosystems that are both products and services, such as Gmail and Office365. – Sipes, Thunderbird
At the center of the announcement is Thundermail, a fully open-source, privacy-respecting email service designed to align with Thunderbird's long-standing values. The platform will support email, calendars, and contact management under domains like thundermail.com and tb.pro, with users also allowed to bring their own domains at launch. The service explicitly promises no ads, no AI training on user data, and no user tracking — positioning itself as a meaningful alternative to mainstream email providers.
Supporting this core offering is a trio of companion services under the Thunderbird Pro banner:
- Thunderbird Appointment is a lightweight scheduling tool currently in closed beta. It allows users to share availability via a link, offering a streamlined alternative to bloated or proprietary calendar tools. The project is publicly developed and has already garnered significant community involvement.
- Thunderbird Send revives the concept of Firefox Send, Mozilla's now-defunct file-sharing service, but rebuilt with a focus on direct, end-to-end encrypted transfers between users. Currently in alpha testing, it allows the secure exchange of large files without exposing user data to third parties. The new version of Send emphasizes minimal reliance on shared download links and will enter closed beta soon.
- Thunderbird Assist, still in development, will introduce AI-powered features using Flower AI's federated learning framework. Crucially, all processing will occur on-device or via a confidential remote compute model similar to Apple's Private Cloud Compute. Assist features will be opt-in only, and Thunderbird has committed to never training AI models on user data. The source code repository will be made public in the near future.
Thunderbird's move into cloud services reflects growing user expectations for seamless integration between communication tools and hosted services. The team acknowledges the competitive disadvantage posed by platforms like Google Workspace and Microsoft Office365, which offer both software and tightly integrated backend services. With Thunderbird Pro, the goal is to offer a modular, fully open-source alternative that users can run themselves or subscribe to — without any form of vendor lock-in.
To fund these services, Thunderbird will introduce paid subscription tiers initially, with a free limited-use tier planned once a sustainable user base is established. This mirrors models seen with ProtonMail and other privacy-centric service providers. Importantly, Thunderbird Pro is a completely opt-in system and will not interfere with or alter the standalone Thunderbird client unless users choose to adopt the new services.
Where’s this going to be hosted / where is the residence of the commercial entity taking payment ?