Mozilla is expanding its Thunderbird email client into a full-fledged communications platform, launching Thundermail and Thunderbird Pro to compete directly with Gmail by Alphabet Inc.'s GOOG GOOGL Google and Microsoft Corp.'s MSFT subscription service, Microsoft 365.
What Happened: On Wednesday, Mozilla announced the overhaul of Thunderbird Pro, which includes Thunderbird Appointment, a scheduling tool for sharing calendar links; Thunderbird Send, a revival of the discontinued Firefox Send; and Thunderbird Assist, an AI-powered writing assistant developed with Flower AI.
Unlike traditional services, Thunderbird Pro underscores local AI processing to ensure privacy.
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The company is also launching Thundermail, which will use the open-source Stalwart stack and allow users to choose between thundermail.com and tb.pro domains for email hosting.
“Heading to thundermail.com, you will see a signup page for the beta waitlist. Please add your name to it,” said Ryan Sipes, Managing Director, Product Thunderbird.
Will It Be Free? No. Initially, Mozilla will charge for these services, especially features like Thunderbird Send (since storage is expensive). The service will be available for free to select contributors. However, once they have a stable user base, the company plans to introduce free tiers with limitations (e.g., reduced storage).
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Why It Matters: Thunderbird has been losing users over time—its active monthly installs have dropped from 17.7 million in 2020 to 16.2 million in 2025.
By adding Thundermail and new paid features, Mozilla hopes to build a sustainable business model and attract users who value privacy, transparency, and open-source software.
“Thunderbird loses users each day to rich ecosystems that are both clients and services, such as Gmail and Office365,” stated Sipes, adding, “It is our goal to eventually have a similar offering so that a 100% open source, freedom-respecting alternative ecosystem is available for those who want it.”
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Disclaimer: This content was partially produced with the help of Benzinga Neuro and was reviewed and published by Benzinga editors.
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