Mozilla launching "Thundermail" email service to take on Gmail, Microsoft 365

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Thunderbird is getting a bunch of new features

Thunderbird
(Image credit: Mozilla)
  • Mozilla takes on Gmail, Microsoft 365 with range of new features
  • Thunderbird Pro includes Appointment, Send and Thundermail
  • A new AI writing tool is also coming with local processing

Mozilla is turning its Thunderbird open source email client into a full communications platform with the launch of Thundermail and Thunderbird Pro.

The expansion of Mozilla's email services aims to compete with rival ecosystems like Gmail and Microsoft 365, which are more rich in features, except Mozilla’s offering stands out for its open source values of privacy, freedom, transparency and user respect.

“Thunderbird loses users each day to rich ecosystems that are both clients and services,” Ryan Sipes, Managing Director for Product Thunderbird confirmed as he expressed the ‘why’ behind Thunderbird’s expansion.

Thunderbird is about to get an overhaul

The Thunderbird database says its number of active monthly installs has dropped from 17.7 million in late December 2020 to 16.2 million in late March 2025, with the mail app struggling to keep up with the industry’s main players like Gmail.

With the launch of Thunderbird Pro, Mozilla is adding Thunderbird Appointment, a new scheduling tool for sharing calendar links; Thunderbird Send, a rebuild of the discontinued Firefox Send; and Thunderbird Assist, a new AI-powered writing tool enabled via a partnership with Flower AI that is intended to do the processing locally to eliminate privacy concerns.

The final launch will be Thundermail, an email hosting service using the open-source Stalwart stack. Usrs will be able to pick between thundermail.com and tb.pro domains.

Apart from consistent community contributors who will be able to get early access for free, Sipes confirmed Mozilla would ultimately end up charging for the features, such as Send which requires storage, an expensive commodity.

“Once we have a strong enough user base that the services appear to be sustainable, we will open up free tiers with limitations, such as less storage or the like,” Sipes added.

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Craig Hale
Craig Hale

With several years’ experience freelancing in tech and automotive circles, Craig’s specific interests lie in technology that is designed to better our lives, including AI and ML, productivity aids, and smart fitness. He is also passionate about cars and the decarbonisation of personal transportation. As an avid bargain-hunter, you can be sure that any deal Craig finds is top value!

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