The Best Open Source Microsoft Outlook AlternativesTop Email Clients & Calendar Apps like Microsoft Outlook

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

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Microsoft Outlook alternatives are mainly Email Clients but may also be Calendar Apps or Todo List Managers. Other popular filters includes Windows + Free. Filter by these or use the filter bar below if you want a narrower list of alternatives or looking for a specific functionality of Microsoft Outlook.

Microsoft Outlook

394

Email Client
Paid • Proprietary

Manage emails, calendars, contacts, and tasks with an intuitive interface. Features smart inbox, file management, and third-party app integration.

More about Microsoft Outlook

Microsoft Outlook alternatives page was last updated Oct 11, 2024

Thunderbird
Thunderbird is a free, open source, cross-platform e-mail, news and instant messaging client. The project strategy is modeled after Mozilla Firefox.
90 Thunderbird alternatives
License model
- Free • Open Source
Application types
- Email Client
- Calendar App
Platforms
- Mac
- Windows
- Linux
- BSD
- AppImageHub
- Snapcraft
- Flathub
- PortableApps.com
- Haiku
- Homebrew
- Chocolatey
Top Thunderbird Features
1. Extensible by Plugins/Extensions
2. Multiple Account support
3. IMAP Support
4. Calendar Integration
5. SMTP Support
6. Email Organizer
7. Add-ons
8. Built-in RSS reader
9. Instant Messaging
10. POP3 Support
11. Graphical User Interface
12. Customizable
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Thunderbird VS Microsoft Outlook
Is Thunderbird a good alternative to Microsoft Outlook?
Comments about Thunderbird as an Alternative to Microsoft Outlook

John Fastman
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 •Jan 1, 2017
12
wookahn624
For me it is the only alternative to Outlook, if you want power of Outlook and open source there is just no other app.
Top positive comment •Jun 27, 2018
7
Guest
The interface is just impossible for many people to use.
Top negative comment •Aug 5, 2020
16
Shaz Shah
I remember when I first used Thunderbird, many years ago, as I'd rather have a single interface for productivity. But the interface through me off and I never got on with the editor. Coming back to it now, it's fresher and smoother. Absolutely love it. In my opinion this is the only true alternative to Outlook. Then there's the bonus of extensions to further enhance it. Though, I'd like to see further improvements to the calendar integration.
Positive comment •May 31, 2024
0
s0raz
I would rather Thunderbird over Outlook because it's open source.
Positive comment •Nov 7, 2022
0
Show more comments
5 of 15 comments
- Most users think Thunderbird is a great Microsoft Outlook alternative.
- Thunderbird is the most popular Windows, Mac & Linux alternative to Microsoft Outlook.
- Thunderbird is the most popular Open Source & free alternative to Microsoft Outlook.
- Thunderbird is Free and Open SourceMicrosoft Outlook is Paid and Proprietary
- Thunderbird is CustomizableMicrosoft Outlook is not according to our users

K-9 Mail
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.
43 K-9 Mail alternatives
License model
- Free • Open Source
Application type
- Email Client
Platforms
- Android
- Android Tablet
- F-Droid
+3
Top K-9 Mail Features
1. Ad-free
2. IMAP Support
3. Multiple Account support
4. Configurable
5. Privacy focused
6. POP3 Support
7. One view multiple accounts
8. PGP Encryption
9. Lightweight
10. Unified inbox
11. No Tracking
12. End-to-End Encryption
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K-9 Mail VS Microsoft Outlook
Is K-9 Mail a good alternative to Microsoft Outlook?
Comments about K-9 Mail as an Alternative to Microsoft Outlook

John Fastman
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 •Jan 10, 2017
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 •Feb 22, 2017
1
- Most users think K-9 Mail is a great Microsoft Outlook alternative.
- K-9 Mail is the most popular Android & Android Tablet alternative to Microsoft Outlook.
- K-9 Mail is Free and Open SourceMicrosoft Outlook is Paid and Proprietary
- K-9 Mail is Privacy focused and LightweightMicrosoft Outlook is not according to our users

Evolution
Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.
78 Evolution alternatives
License model
- Free • Open Source
Application types
- Email Client
- Calendar App
Platforms
- Linux
- BSD
- Flathub
- S/MIME
- GNOME
- OpenPGP
+4
Top Evolution Features
1. Calendar Integration
2. Contacts
3. CalDAV Support
4. Calendar View
5. Ad-free
6. Spam Filter
7. Multiple Account support
8. Sync with Google Calendar
9. Extensible by Plugins/Extensions
10. Dark Mode
11. Works Offline
12. GPG Encryption
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Evolution VS Microsoft Outlook
Is Evolution a good alternative to Microsoft Outlook?
Comments about Evolution as an Alternative to Microsoft Outlook

Guest
It runs on Linux and you still have content if you are offline.
Top positive comment •Nov 7, 2021
2
Guest
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.
Top positive comment •Sep 9, 2018
2
Guest
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 •Jan 18, 2020
-1
Guest
I've found it better than thunderbird and it can work with exchange just with one free plugin
Positive comment •Jan 17, 2020
0
Guest
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 •Jul 14, 2018
1
- Most users think Evolution is a great Microsoft Outlook alternative.
- Evolution is Free and Open SourceMicrosoft Outlook is Paid and Proprietary

Mailspring
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
License model
- Freemium • Open Source
Application type
- Email Client
Platforms
- Mac
- Windows
- Linux
- Arch Linux
- Fedora
- Ubuntu
+1
Top Mailspring Features
1. Unified inbox
2. Multiple Account support
3. Dark Mode
4. Customizable
5. Email tracking
6. User friendly
7. Snooze Mail
8. Ad-free
9. Theme Customization
10. Support for Themes
11. Email Organizer
12. Extensible by Plugins/Extensions
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Mailspring VS Microsoft Outlook
Is Mailspring a good alternative to Microsoft Outlook?
Comments about Mailspring as an Alternative to Microsoft Outlook

Paul
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.
Positive comment •Feb 7, 2023
0
Guest
Speed of work, good connection to the mail server, speed search.
Positive comment •Jun 12, 2021
0
Guest
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 •Jul 3, 2019
0
- Most users think Mailspring is a great Microsoft Outlook alternative.
- Mailspring is Freemium and Open SourceMicrosoft Outlook is Paid and Proprietary
- Mailspring is CustomizableMicrosoft Outlook is not according to our users

Geary
Geary is an email application built around conversations, for the GNOME 3 desktop.
50 Geary alternatives
License model
- Free • Open Source
Application type
- Email Client
Platforms
- Linux
- BSD
- Flathub
- GNOME
- Flatpak
Top Geary Features
1. Multiple Account support
2. Conversational email approach
3. Dark Mode
4. Gmail integration
5. IMAP Support
6. Lightweight
7. Spam Filter
8. Ad-free
9. Email Organizer
10. Privacy focused
11. Labels for content
12. SMTP Support
Show all NaN Geary features ▾
Geary VS Microsoft Outlook
Is Geary a good alternative to Microsoft Outlook?
Comments about Geary as an Alternative to Microsoft Outlook

Guest
Beatiful frontend Stable working Advanced features
Positive comment •Sep 26, 2020
1
- Most users think Geary is a great Microsoft Outlook alternative.
- Geary is Free and Open SourceMicrosoft Outlook is Paid and Proprietary
- Geary is Lightweight and Privacy focusedMicrosoft Outlook is not according to our users

FairEmail
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.
44 FairEmail alternatives
+5
License model
- Freemium • Open Source
Application type
- Email Client
Platforms
- Android
- Android Tablet
- F-Droid
Top FairEmail Features
1. Privacy focused
2. Multiple Account support
3. Customizable
4. Email Notifications
5. PGP Encryption
6. Extensive settings menu
7. IMAP Support
8. Notifications
9. No Tracking
10. Works Offline
11. Ad-free
12. Unified inbox
Show all NaN FairEmail features ▾
FairEmail VS Microsoft Outlook
Is FairEmail a good alternative to Microsoft Outlook?
Comments about FairEmail as an Alternative to Microsoft Outlook

Rasheed AZ
open source, secure, regularly updated
Positive comment •Apr 15, 2020
1
- FairEmail is Freemium and Open SourceMicrosoft Outlook is Paid and Proprietary
- FairEmail is Privacy focused and CustomizableMicrosoft Outlook is not according to our users

Betterbird
Betterbird is a drop-in replacement for Mozilla Thunderbird. Betterbird has more features and more fixed bugs than Thunderbird.
28 Betterbird alternatives
License model
- Free • Open Source
Application types
- Email Client
- Calendar App
Platforms
- Mac
- Windows
- Linux
- Flathub
- Chocolatey
+8
Top Betterbird Features
1. Multiple Account support
2. Privacy focused
3. Lightweight
4. Extensible by Plugins/Extensions
5. Unified inbox
6. Works Offline
7. Ad-free
8. Support for Themes
9. Portable
10. PGP Encryption
11. No Tracking
12. Spam Filter
Show all NaN Betterbird features ▾
Betterbird VS Microsoft Outlook
Is Betterbird a good alternative to Microsoft Outlook?