Open Source Microsoft Outlook Alternatives for Windows

There are many alternatives to Microsoft Outlook for Windows if you are looking for a replacement. The best open source Windows alternative is Thunderbird. If that doesn't suit you, our users have ranked more than 100 alternatives to Microsoft Outlook and 19 are open source and available for Windows so hopefully you can find a suitable replacement. Other interesting open source Windows alternatives to Microsoft Outlook are Betterbird, Mailspring, Claws Mail and Pelton.

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Microsoft Outlook alternatives are mainly Email Clients, but if you're looking for Calendar Apps or Contact Managers you can filter on that. Other popular filters include Windows + Free, Open Source, Linux, Android, Windows + Open Source, Free and EU. 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 Microsoft Outlook.
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Alternatives list

  1. Thunderbird icon

    Thunderbird

     2602 likes

    Cross-platform email client supporting multiple identities, chat, and strong filtering. Extend functionality with add-ons like RSS/Atom feed readers and PGP support.

    95 Thunderbird alternatives

    Cost / License

    Application types

    Platforms

    • Mac
    • Windows
    • Linux
    • Android
    • BSD
    • AppImageHub
    • Snapcraft
    • Flathub
    • PortableApps.com
    • F-Droid
    • Haiku
    • Homebrew
    • Chocolatey
    Thunderbird screenshot 1
     
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    17
    Thunderbird vs Microsoft Outlook Comments
    Top Positive Comment
    John Fastman
    11

    Despite its age, Thunderbird remains the most fully featured email client out there. Various add-ons can extend its functionality, it (now) has a built in calendar and, unlike Outlook, it's free, open source and respects your privacy.

    Top Negative Comment
    Guest
    15

    The interface is just impossible for many people to use.

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

    First, it does allow you to connect Zoom for meetings. Second, support is slow or provides little information.

    Review by a new / low-activity user.
    3 of 17 comments
    • Thunderbird is Free and Open SourceMicrosoft Outlook is Paid and Proprietary
    • Thunderbird is Customizable and Privacy focusedMicrosoft Outlook is not according to our users
  2. Betterbird icon

    Betterbird

     86 likes

    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.

    36 Betterbird alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • Flathub
    • Chocolatey
    Betterbird screenshot 1
     
  4. Mailspring icon

    Mailspring

     117 likes

    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.

    49 Mailspring alternatives

    Cost / License

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • Arch Linux
    • Fedora
    • Ubuntu
    Clean design with integrated search and swipe gestures
     
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    3
    Mailspring vs Microsoft Outlook Comments
    Paul
    Positive
    0

    Since Thunderbird is still bloated and overcomplicated for me on Linux, I'm using Mailspring for the moment. It's good, the interface is nice and it has plenty of features.

    Guest
    Positive
    0

    Beautiful theme options with custom designed themes available. I tried thunderbird a few times but always came back to mailspring. I LOVE the "views" feature that shows you how many times an email was opened and if it was forwarded by the recipient!

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

    Speed of work, good connection to the mail server, speed search.

    Review by a new / low-activity user.
    • Mailspring is Freemium and Open SourceMicrosoft Outlook is Paid and Proprietary
    • Mailspring is CustomizableMicrosoft Outlook is not according to our users
  5. Claws Mail icon

    Claws Mail

     105 likes

    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.

    Cost / License

    • Free
    • Open Source

    Application types

    Platforms

    • Windows
    • Linux
    • BSD
    The main window
     
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    1
    Claws Mail vs Microsoft Outlook Comments
    Guest
    Negative
    -2

    Claws Mail is email only, does not have many of the features of Outlook. Displaying HTML mail is sketchy at best.

    Review by a new / low-activity user.
    • Claws Mail is Free and Open SourceMicrosoft Outlook is Paid and Proprietary
    • Claws Mail is Lightweight, Customizable and Privacy focusedMicrosoft Outlook is not according to our users
  7. Pelton icon

    Pelton

     12 likes

    Pelton is a free, open-source email client that searches your whole mailbox locally, online or off. No telemetry, no servers of ours. Your mail stays on your machine.

    17 Pelton alternatives

    Cost / License

    Application type

    Platforms

    • Windows
    • Mac
    • Linux
    Pelton screenshot 1
     
  8. Aerion icon

    Aerion

     10 likes

    Modern open-source email client supporting unified inbox, IMAP/SMTP, Gmail and Outlook with OAuth2, conversation threading, rich text TipTap composing, CardDAV contact sync, tracking removal, dark mode, color themes, vim-style shortcuts, and a detachable window.

    49 Aerion alternatives

    Cost / License

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • Flathub
    • Flatpak
    Aerion screenshot 1
     
  9. Sylpheed icon

    Sylpheed

     62 likes

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

    44 Sylpheed alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Alerts

    • Discontinued

    Platforms

    • Mac
    • Windows
    • Linux
    • BSD
    • PortableApps.com
    Main screen
     
  10. Mutt icon

    Mutt

     68 likes

    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...

    53 Mutt alternatives

    Cost / License

    • Free
    • Open Source

    Application type

    Platforms

    • Mac
    • Windows
    • Linux
    • Xfce
    Mutt screenshot 1
     
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    3
    Mutt vs Microsoft Outlook Comments
    Guest
    Negative
    1

    It's a console based application without proper calendar support. A key feature of outlook

    Review by a new / low-activity user.
    Aristotle Cajetan
    Positive
    -1

    Powerful configuration is possible with mutt, and vim in the terminal.

    Guest
    Negative
    -1

    mutt is email only, terminal based.

    Review by a new / low-activity user.
    • Mutt is Free and Open SourceMicrosoft Outlook is Paid and Proprietary
  11. Wino Mail icon

    Wino Mail

     8 likes

    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.

    Cost / License

    Application type

    Platforms

    • Windows
    Wino Mail screenshot 1
     
  12. Scribe Mail icon

    Scribe Mail

     8 likes

    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...

    40 Scribe Mail alternatives

    Cost / License

    Application types

    Platforms

    • Mac
    • Windows
    • Linux
    • Haiku
    Main window
     
  13. Trojitá icon

    Trojitá

     17 likes

    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
     
  14. Columba icon

    Columba

     6 likes

    Columba is an email client written in Java, featuring a user-friendly graphical interface with wizards and internalionalization support. Its a powerful mail management tool with features to enhance your productivity and communication.

    Cost / License

    • Free
    • Open Source

    Application type

    Alerts

    • Discontinued

    Platforms

    • Mac
    • Windows
    • Linux
    • BSD
    Columba screenshot 1
     
12 of 19 Microsoft Outlook alternatives