Open Source Thunderbird Alternatives for Windows

There are many alternatives to Thunderbird for Windows if you are looking for a replacement. The best open source Windows alternative is Claws Mail. If that doesn't suit you, our users have ranked more than 50 alternatives to Thunderbird and 18 are open source and available for Windows so hopefully you can find a suitable replacement. Other interesting open source Windows alternatives to Thunderbird are Betterbird, SeaMonkey, Mailspring and Sylpheed.

filter to find the best alternatives

Thunderbird alternatives are mainly Email Clients, but if you're looking for Calendar Apps or Group Chat Apps you can filter on that. Other popular filters include Linux, Open Source, iPhone, Windows, Windows + Open Source, Android and Free. You can also filter by region, for example EU-based alternatives if you prefer software developed in the European Union. These are just examples - use the filter bar below to find more specific alternatives to Thunderbird.
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Alternatives list

  1. Claws Mail icon

    Claws Mail

     106 likes
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    Email and news client on GTK+ foundation featuring quick performance, extensible plugins, secure protocols, advanced filtering, strong folder and contact management, lightweight design, powerful search, customizable interface, multi-language support, and encryption.

    62 Claws Mail alternatives

    Cost / License

    • Free
    • Open Source

    Application types

    Platforms

    • Windows
    • Linux
    • BSD
    The main window
     
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    51
    Comments about Claws Mail as an Alternative to Thunderbird
    Top Positive Comment
    Jonathan DUMONT
    9

    Despite the style, Claws is super fast and allow you to programs it with Perl and Python which is great for marketing automation.

    Top Negative Comment
    Guest
    19

    No HTML compose is the only reason I don't switch to it. We're not in 1980 anymore.

    Review by a new / low-activity user.
    SViN
    2

    I think most people are using gmail accounts or outlook accounts to access their emails. Claws supports Oauth2 to access said accounts but the implementation, is a complete PAIN.

    I can only realistically recommend something like this if your email provider is not forcing Oauth2.

    I would like for the devs to get to work into making the experience of setting up an account with oauth as painless as thunderbird.

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    3 of 8 comments
    Thunderbird Icon
    Claws Mail icon

    • Most users think Claws Mail is a great Thunderbird alternative.

    • Claws Mail is the most popular Windows & Linux alternative to Thunderbird.

    • Claws Mail is Free and Open SourceThunderbird is also Free and Open Source
    • Claws Mail is LightweightThunderbird is not according to our users
  2. Betterbird icon

    Betterbird

     70 likes
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    Betterbird, a soft fork of Mozilla Thunderbird, improves user experience with advanced features, bug fixes, security patches, and multi-row descriptions similar to Outlook. Compatible with multiple platforms and can be used alongside Thunderbird, sharing the same profile.

    28 Betterbird alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • Flathub
    • Chocolatey
    Betterbird screenshot 1
     
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    5
    16
    Comments about Betterbird as an Alternative to Thunderbird
    Top Positive Comment
    Sam Lander
    3

    Betterbird does everything that Thunderbird does (it's a soft fork), while improving bugs and features.

    Because it's a soft fork, it retains the security implementations of Thunderbird.

    Thunderbird actually implements many of the bug fixes created by Betterbird, but at a much slower pace.

    drummer_nrg
    Positive
    1

    Betterbird is actively updated by a previous Thunderbird developer and is a fully compatible fork of Thunderbird which fixes some outstanding bugs. My add-ons like keepassxc-mail work fine!

    Guest
    Positive
    2

    It has many fixes for long existing bugs

    Review by a new / low-activity user.
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    3 of 5 comments
    Thunderbird Icon
    Betterbird icon

    • Almost everyone thinks Betterbird is a great Thunderbird alternative.

    • Betterbird is the most popular Mac alternative to Thunderbird.

    • Betterbird is Free and Open SourceThunderbird is also Free and Open Source
    • Betterbird is LightweightThunderbird is not according to our users
  4. SeaMonkey icon

    SeaMonkey

     241 likes
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    Web-browser, advanced e-mail, newsgroup and feed client, IRC chat, and HTML editing in one application. Itis built on the open source Mozilla Gecko engine, the same code which underlies Thunderbird and is the base for the Firefox browser.

    185 SeaMonkey alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • BSD
    • PortableApps.com
    SeaMonkey screenshot 1
     
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    4
    43
    Comments about SeaMonkey as an Alternative to Thunderbird
    Guest
    Positive
    21

    SeaMonkey is both a WEB BROWSER and EMAIL CLIENT. It's the successor of Mozilla Application Suite or Netscape Communicator, resp. Further it includes also a news client program, an HTML editor (SeaMonkey Composer) and an IRC client (ChatZilla).

    Review by a new / low-activity user.
    apostolfaliagas
    Positive
    15

    It has all of Thunderbird's features and many more.

    Guest
    Negative
    0

    Unfortunately doesn't support synchronization with CardDAV address books.

    Review by a new / low-activity user.
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    3 of 4 comments
    Thunderbird Icon
    SeaMonkey icon

    • Some users think SeaMonkey is a great Thunderbird alternative, some don't.

    • SeaMonkey is Free and Open SourceThunderbird is also Free and Open Source
    • SeaMonkey is LightweightThunderbird is not according to our users
  5. Mailspring icon

    Mailspring

     113 likes
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    Boost your productivity and send better email with Mailspring, a beautiful, fast email client for Mac, Windows, and Linux. Mailspring is free to use and an optional pro version adds read receipts, send later, reminders and more.

    43 Mailspring alternatives

    Cost / License

    • Freemium (Subscription)
    • Open Source

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • Arch Linux
    • Fedora
    • Ubuntu
    Clean design with integrated search and swipe gestures
     
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    7
    29
    Comments about Mailspring as an Alternative to Thunderbird
    Top Positive Comment
    3psilon
    1

    Great alternative, especially for casual users. Simple, streamlined UI, feels fresh.

    Top Negative Comment
    Guest
    60

    Need to create an account on a third-party company to access your email.

    Review by a new / low-activity user.
    Matt Schaefer
    Negative
    0

    Unable to even find an address book or ability to import a csv file from previous mail client. You lose me when things are made so "modern-clean" that I have to consult a manual or Google things.

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    3 of 7 comments
    Thunderbird Icon
    Mailspring icon

    • Most users think Mailspring is a great Thunderbird alternative.

    • Mailspring is Freemium and Open SourceThunderbird is Free and Open Source
  6. Sylpheed icon

    Sylpheed

     62 likes
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    Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).

    42 Sylpheed alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Alerts

    • Discontinued

    Platforms

    • Mac
    • Windows
    • Linux
    • BSD
    • PortableApps.com
    Main screen
     
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    1
    17
    Comments about Sylpheed as an Alternative to Thunderbird
    Guest
    Negative
    3

    It doesn't encrypt password storage and doesn't have Master Password function

    Review by a new / low-activity user.
    Thunderbird Icon
    Sylpheed icon

    • Most users think Sylpheed is a great Thunderbird alternative.

    • Sylpheed is Free and Open SourceThunderbird is also Free and Open Source
    • Sylpheed is LightweightThunderbird is not according to our users
  7. Mutt icon

    Mutt

     68 likes
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    Mutt is a small but very powerful text-based mail client for Unix operating systems. Some of its features are: color support, message threading, MIME support (including RFC2047 support for encoded headers), PGP/MIME (RFC2015), various features to support mailing lists, including...

    51 Mutt alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • Xfce
    Mutt screenshot 1
     
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    2
    24
    Comments about Mutt as an Alternative to Thunderbird
    Guest
    Negative
    17

    Thunderbird users want a GUI mail application. Mutt is a command line mail application. They are both good and both popular, but very much apples and oranges.

    Review by a new / low-activity user.
    Guest
    Negative
    0

    Mutt's a great email client for your terminal, not a GUI app like Thunderbird.

    Review by a new / low-activity user.
    Thunderbird Icon
    Mutt icon

    • Most users think Mutt is a great Thunderbird alternative.

    • Mutt is Free and Open SourceThunderbird is also Free and Open Source
  9. Wino Mail icon

    Wino Mail

     8 likes
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    Wino is a lightweight native mail client for Windows 10/11. It is still in active development. Main motivation for this project is to replace Mail & Calendar for Windows with modern Windows design without using web technologies for speed.

    21 Wino Mail alternatives

    Cost / License

    • Freemium (Pay once)
    • Open Source

    Application type

    Platforms

    • Windows
    Wino Mail screenshot 1
     
  10. ElectronMail icon

    ElectronMail

     24 likes
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    ElectronMail is an Electron-based unofficial desktop client for ProtonMail and Tutanota end-to-end encrypted email providers. The app aims to provide enhanced desktop user experience enabling features that are not supported by the official in-browser web clients.

    Cost / License

    • Free
    • Open Source

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • ProtonMail
    • Electron / Atom Shell
    • Tutanota
    ElectronMail screenshot 1
     
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    2
    Comments about ElectronMail as an Alternative to Thunderbird
    Guest
    Negative
    17

    Thunderbird connects with servers that use standard protocols and with servers for which a plugin was developed. ElectronMail works with ProtonMail ONLY and was specifically designed for this provider. Tutanota support is deprecated since July 2019.

    Review by a new / low-activity user.
    Guest
    Negative
    3

    It's only used for one provider

    Review by a new / low-activity user.
    Thunderbird Icon
    ElectronMail icon
    • ElectronMail is Free and Open SourceThunderbird is also Free and Open Source
  11. Trojitá icon

    Trojitá

     17 likes
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    Trojitá, is a fast Qt IMAP e-mail client that respects open standards and facilitates modern technologies. Trojitá values vendor-neutrality that IMAP provides and is committed to be as interoperable as possible.

    Cost / License

    • Free
    • Open Source

    Application type

    Alerts

    • Discontinued

    Platforms

    • Windows
    • Linux
    Home
     
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    7
  12. LucaMail icon

    LucaMail

     9 likes
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    LucaMail is an open source, cross-platform email client. LucaMail is developed to provide cross-platform alternative to Email Clients that are really exists. LucaMail focuses on modern technologies as well as maintaining a user-friendly UI.

    70 LucaMail alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Alerts

    • Discontinued

    Platforms

    • Mac
    • Windows
    • Linux
    LucaMail screenshot 1
     
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    1
    Comments about LucaMail as an Alternative to Thunderbird
    sp4mmed
    Negative
    -1

    The lack of POP support means this is useless for my purposes. Since Thunderbird DOES support POP this means LucaMail is NOT an alternative.

    Thunderbird Icon
    LucaMail icon
    • LucaMail is Free and Open SourceThunderbird is also Free and Open Source
  13. Scribe Mail icon

    Scribe Mail

     7 likes
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    Scribe is a small portable email client with an intergrated contact database and calendar. It supports all the major internet mail protocols and uses international standards where possible. Scribe doesn't required installing or uninstalled and can be used from a removable...

    Cost / License

    • Free
    • Open Source

    Application types

    Platforms

    • Mac
    • Windows
    • Linux
    • Haiku
    Main window
     
  14. Nylas Mail Lives icon

    Nylas Mail Lives

     3 likes
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    Nylas Mail Lives is a fork of Nylas Mail that fixes many longstanding issues, improves the client experience, and is committed to publish new releases.

    Cost / License

    • Free
    • Open Source

    Application type

    Alerts

    • Discontinued

    Platforms

    • Mac
    • Windows
    • Linux
    • Self-Hosted
    Nylas Mail Lives screenshot 1
     
12 of 18 Thunderbird alternatives