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Open Source Microsoft Outlook Alternatives

The best open source alternative to Microsoft Office Outlook is Thunderbird. If that doesn't suit you, our users have ranked more than 100 alternatives to Microsoft Office Outlook and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Microsoft Office Outlook are Evolution, K-9 Mail, Mailspring and FairEmail.

Microsoft Office Outlook 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 Microsoft Office Outlook.
This page was last updated Feb 23, 2022
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Microsoft Outlook, part of the Microsoft Office Suite (not to be confused with...

Learn more about Microsoft Office Outlook

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

    Thunderbird vs Microsoft Office Outlook opinions
    Most users think Thunderbird is a great alternative to Microsoft Office Outlook.
     all • positive • negative      relevance • date

    Seems to be more secure than Microsoft alternatives and more easily updatable.

    Top positive comment  about 5 years ago
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    11
    JohnFastman

    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 positive comment  over 5 years ago
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    10

    The interface is just impossible for many people to use.

    Top negative comment  almost 2 years ago
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    12

    I transitioned all ove my computers from Windows to Linux. I had 4 computers so I used four different distributions with different linux bases, Debian and Arch. Thunderbird worked perfectly. The email client is awesome, I think they should devote more development efforts to calender and task management integration.

    Positive comment almost 2 years ago
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    2
    sangwenobdi

    It can access email server just as outlook

    Positive comment almost 2 years ago
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    1
    Can202

    ThunderBird es la mejor alternativa open source, ya que puedes personalizarlo, mi recomendación es usar la extención CheckBox, Thunderbird junto a CheckBox (extensión), la mejor APP para Mail

    Positive comment almost 2 years ago
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    2

    Thunderbird is best that other application listed here and GUI is also nice

    Positive comment about 2 years ago
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    3
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    7 of 13 comments
  2. Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.

    Evolution vs Microsoft Office Outlook opinions
    Most users think Evolution is a great alternative to Microsoft Office Outlook.

    It runs on Linux and you still have content if you are offline.

    Top positive comment  8 months ago
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    1

    I've found it better than thunderbird and it can work with exchange just with one free plugin

    Top positive comment  over 2 years ago
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    0

    This would be the best alternative, except that it requires the Gnome desktop, so users of other desktop environments need to look elsewhere.

    Positive comment over 2 years ago
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    -1

    Fast and User friendly. Light-weight and classic menus really give a touch of old classic office 2003. Easy integration of mails especially exchange mails without facing any bottlenecks.

    Positive comment almost 4 years ago
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    1

    Support for EWS allows me to connect to exchange and get all the benefits like contacts and calendar I wouldn't so easily get on Thunderbird. Also it nicely integrates with the built in Ubuntu calendar as well which is a big plus.

    Positive comment almost 4 years ago
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    1


  3. 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 Microsoft Office Outlook opinions
    Most users think K-9 Mail is a great alternative to Microsoft Office Outlook.
    JohnFastman

    Not the prettiest, but it's open source (trustworthy), free, privacy-respecting and very functional. My go-to Android email client. I cannot hesitate less in recommending it.

    Positive comment over 5 years ago
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    4
    Online_Purchases1

    Deletes e-mail from the server even when underground in NYC subway. Makes life so easy to delete e-mails while on the train When surfacing, K-9 syncs with the server and POOF....those unwanted e-mails are gone from the server.

    Positive comment over 5 years ago
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    1
  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 Microsoft Office Outlook opinions
    Most users think Mailspring is a great alternative to Microsoft Office Outlook.

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

    Positive comment about 1 year ago
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    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!

    Positive comment almost 3 years ago
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    0
  5. 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 Microsoft Office Outlook opinions
    pros, cons and recent comments
    RasheedAZ

    open source, secure, regularly updated

    Positive comment about 2 years ago
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    1


  6. Geary is an email application built around conversations, for the GNOME 3 desktop.

    Geary vs Microsoft Office Outlook opinions
    Most users think Geary is a great alternative to Microsoft Office Outlook.

    Beatiful frontend Stable working Advanced features

    Positive comment almost 2 years ago
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    1
  7. 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 Microsoft Office Outlook opinions
    pros, cons and recent comments

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

    Negative comment over 2 years ago
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    -2
  8. Kontact - KMail

    • FreeOpen Source
    • Linux
    • BSD

    KMail is the email component of Kontact, the integrated personal information manager of KDE. Kontact is a personal information manager and groupware software suite for KDE. It supports calendars, contacts, notes, to-do lists, news, and email.

    Kontact - KMail vs Microsoft Office Outlook opinions
    Almost everyone thinks Kontact - KMail is a great alternative to Microsoft Office Outlook.

    This is a very integrated suite of programs offering all the functionality of Outlook. Native to KDE's Plasma desktop environment.

    Positive comment over 2 years ago
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    1
  9. Mutt is a small but very powerful text-based mail client for Unix operating systems.

    Mutt vs Microsoft Office Outlook opinions
    pros, cons and recent comments

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

    Negative comment 12 months ago
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    1
    scholasticphilosopher

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

    Positive comment over 4 years ago
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    -1

    mutt is email only, terminal based.

    Negative comment over 2 years ago
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    -1
  10. Personal Information Manager (Mail, Contact, Calendar and more).

Showing 10 of 37 alternatives