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Open Source Thunderbird Alternatives

The best open source alternative to Thunderbird is K-9 Mail. If that doesn't suit you, our users have ranked more than 50 alternatives to Thunderbird and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Thunderbird are Evolution, Claws Mail, Mailspring and Geary.

Thunderbird alternatives are mainly Email Clients but may also be Calendar Apps or Email Organizers. Filter by these if you want a narrower list of alternatives or looking for a specific functionality of Thunderbird.
This page was last updated Jun 7, 2022
Thunderbird
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  • FreeOpen Source
  • Mac
  • Windows
  • Linux
  • BSD
  • PortableApps.com
  • Haiku

Thunderbird is a free, open source, cross-platform e-mail, news and instant messaging client. The project strategy is...

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  1. K-9 is an open source email client for Android with multi-folder sync, email signatures, Bcc-to-self, return-address configuration, keyboard shortcuts, Exchange Support, message flagging, IMAP deletes, saving attachments, configurable notifications and more.

    K-9 Mail vs Thunderbird opinions
    Most users think K-9 Mail is a great alternative to Thunderbird.
     all • positive • negative      relevance • date

    K-9 Mail works on Android, can use POP3 or IMAP and is easy to use. It's open source with no adverts.

    Top positive comment  about 5 years ago
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    12

    open source, stable, essentially bug free, low on resource need, just e-mail without "cool" extra functions you never use.

    Top positive comment  about 4 years ago
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    8

    wrong platform. K-9 is for android, Thunderbird is not, so K9 is not a valid alternative for Thunderbird users

    Top negative comment  over 1 year ago
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    15
    LinuxDoge

    I used FairEmail before, which is also awesome. K9Mail has awesome integration of "OpenKeyChain", which is also FOSS and enables PGP encryption also apart from the mail program, so actually an advantage.

    K9-Mail has easy switches between profiles, a stunning modern GUI and easy support for "PGP encrypt" vs "just sign" with one click.

    Positive comment 3 months ago
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    0
    GadGray

    K9 is only an alternative for android devices.

    Negative comment 7 months ago
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    2
    Philippe_Hellmuller

    So far, I dislike the presentation which doesn't allow me to have a global view on my messages and possibly even different accounts. I'm also missing contacts and contact groups. The application looks very much like Outlook that I don't appreciate because of its presentation.

    Positive comment over 1 year ago
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    -1
    Bacma

    Very pratic and user-friend, but it is too much simple, not personalizable.

    Positive comment about 2 years ago
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    -2
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    7 of 17 comments
  2. Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.

    Evolution vs Thunderbird opinions
    Most users think Evolution is a great alternative to Thunderbird.

    Has a nice Gui, works fast and has many options. Still some functions are not intuitive. Good alternative to Thunderbird

    Positive comment about 1 year ago
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    0

    well, I use cinnamon desktop, Thunderbird does not display 24 hour format but AM/PM for starters. Also, I use the built-in acount manager and Thunderbird does not "talk" with that as well.. Evolution does sync my CALDAV and CARDDAV from this. Thunderbird needs plugins for this and these plugins also make Thunderbird unstable (lightning). Since I like to keep things "clean", Evolution is my software of choice ATM...

    Positive comment over 2 years ago
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    -1


  3. Claws Mail is an email client (and news reader), based on GTK+, featuring

    Quick response Graceful, and sophisticated interface Easy configuration, intuitive operation Abundant features Extensibility Robustness and stability.
    Claws Mail vs Thunderbird opinions
    Most users think Claws Mail is a great alternative to Thunderbird.
    3psilon

    It's a good, lightweight alternative, but the UI is clunky and it misses HTML message composing. You have been warned!

    Top positive comment  almost 5 years ago
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    14

    Much faster than thunderbird which cloaks on weak machines.

    Top positive comment  over 4 years ago
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    6

    very good alternative under linux. I can not say the same under windows since fancy plugin is very buggy.

    Positive comment about 2 years ago
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    -1
    jodumont

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

    Positive comment almost 3 years ago
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    8

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

    Negative comment almost 4 years ago
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    14

    Small and quick and not flooded with choices!

    Positive comment about 6 years ago
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    2

    I like it because of easily customizable key bindings.

    Positive comment about 6 years ago
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    0
  4. 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.

    Mailspring vs Thunderbird opinions
    This alternative is disputed. Mailspring is still a legitimate alternative to Thunderbird, but it might have issues that some users think are important.
    3psilon

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

    Top positive comment  about 4 years ago
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    1

    Very simple, perfect IU and possibility to follow what happen to your emails.

    Top positive comment  over 4 years ago
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    -1
    riskaasmara

    Simple, more streamlined UI and easily customizable.

    Positive comment over 3 years ago
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    4

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

    Negative comment almost 4 years ago
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    52
    peterbro

    nice interface (if you are talking about the feature, kcontact/kmail is the best, but this has a nice interface)

    Positive comment over 4 years ago
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    -3
    bengotow

    Supports Linux and all IMAP providers, offers shortcut customization, extensible via plugins.

    Positive comment over 4 years ago
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    -3
  5. Geary is an email application built around conversations, for the GNOME 3 desktop.

    Geary vs Thunderbird opinions
    Some users think Geary is a great alternative to Thunderbird, some don't.

    Doesn't have an address book

    Negative comment about 5 years ago
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    1

    Easy to set up. Thunderbird doesn't connect anymore with hotmail and yahoo. No address book.

    Positive comment almost 5 years ago
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    -21

    Only IMAP. No support for local folders.

    Negative comment almost 4 years ago
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    1


  6. 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.

    SeaMonkey vs Thunderbird opinions
    Almost everyone thinks SeaMonkey is a great alternative to Thunderbird.

    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).

    Positive comment over 4 years ago
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    20

    Unfortunately doesn't support synchronization with CardDAV address books.

    Negative comment 3 months ago
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    0
    apostolfaliagas

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

    Positive comment over 4 years ago
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    14

    More of a web browser than an email client

    Negative comment about 3 years ago
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    -7
  7. FairEmail is a privacy-focused email client with a setup wizard that helpfully walks you through the steps to use it with any email provider. There are many privacy settings including encryption via OpenPGP and S/MIME and reformatted emails to avoid phishing.

    FairEmail vs Thunderbird opinions
    Most users think FairEmail is a great alternative to Thunderbird.

    wrong platform. FairEmail is not an alternative for Thunderbird users because it only runs on android. Thunderbird is for desktop operating systems only.

    Negative comment over 1 year ago
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    -5
  8. Mutt is a small but very powerful text-based mail client for Unix operating systems.

    Mutt vs Thunderbird opinions
    Most users think Mutt is a great alternative to Thunderbird.

    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.

    Negative comment about 2 years ago
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    15
  9. Delta Chat

    • FreeOpen Source
    • Mac
    • Windows
    • Linux
    • Android
    • iPhone
    • Android Tablet
    • FLATHUB
    • F-Droid

    Delta Chat looks and feels like other popular messenger apps, but does not involve centralized control, tracking or selling you, friends, colleagues or family out to large organizations. "Privacy by Design" has never been more fun.

    Delta Chat vs Thunderbird opinions
    pros, cons and recent comments
    GeminiDomino

    It doesn't let you read existing email, it's a chat client that uses an IMAP mail server as its back end

    Negative comment 8 months ago
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    2
    BadTek

    More like an IM, not a full-featured email client.

    Negative comment 7 months ago
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    1
  10. Sylpheed

    • FreeOpen Source
    • Mac
    • Windows
    • Linux
    • BSD
    • PortableApps.com

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

    Sylpheed vs Thunderbird opinions
    Most users think Sylpheed is a great alternative to Thunderbird.

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

    Negative comment about 3 years ago
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    3
Showing 10 of 40 alternatives