The Best Open Source Microsoft Outlook AlternativesTop Email Clients & Calendar Apps like Microsoft Outlook in 2023

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 K-9 Mail, Evolution, Mailspring and FairEmail.

Microsoft Office Outlook alternatives are mainly Email Clients but may also be Calendar Apps or Todo List Managers. Filter by these if you want a narrower list of alternatives or looking for a specific functionality of Microsoft Office Outlook.

Microsoft Office Outlook alternatives page was last updated

Microsoft Office Outlook

391

Paid • Proprietary
Email Client

Microsoft Outlook, part of the Microsoft 365 (Office) (not to be confused with...

More about Microsoft Office Outlook

Thunderbird
Is this is a good alternative?
Yes
No
Free • Open Source
Email Client
Calendar App
Mac
Windows
Linux
BSD
AppImageHub
Snapcraft
Flathub
PortableApps.com
Haiku
Homebrew
Chocolatey
93 Thunderbird alternatives
Thunderbird is a free, open source, cross-platform e-mail, news and instant messaging client. The project strategy is modeled after Mozilla Firefox.
- - Thunderbird is the most popular Windows, Mac & Linux alternative to Microsoft Office Outlook.
- - Thunderbird is the most popular Open Source & free alternative to Microsoft Office Outlook.
Suggest and vote on features
Thunderbird Features
1. Extensible by Plugins/ExtensionsThunderbird can be extended with add-ons, plugins and extensions.
2. Multiple Account supportThunderbird support multiple accounts without the need to logout and login
3. Calendar IntegrationThunderbird lets you sync your tasks and events with your calendar application.
4. Email OrganizerThunderbird allows you to take control of your inbox by filtering and control tools.
5. Dark ModeThunderbird supports dark mode for comfortable usage in low light conditions.
6. OpenPGPThunderbird supports OpenPGP, a standard of PGP encryption that is open-source for public use.
7. GPG EncryptionThunderbird supports GPG (aka GnuPG) for encryption of things like emails, messages, files, etc.
8. PortableThunderbird can be used from a USB stick or similar with no prior installation.
9. Import/Export OPML FeedsImport and export your feed subscriptions into OPML format with Thunderbird.
IMAP Support
SMTP Support
FOSS
Add-ons
Built-in RSS reader
POP3 Support
Intuitive
Graphical User Interface
Customizable
Integrated Web Browser
Comments about Thunderbird as a Alternative to Microsoft Office Outlook
Most users think Thunderbird is a great Microsoft Office Outlook alternative.
all • positive • negative relevance • date
Guest
Thunderbird is best that other application listed here and GUI is also nice
Top positive comment•
5

Guest
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.
Top positive comment•
2

Guest
The interface is just impossible for many people to use.
Top negative comment•
13

s0raz
I would rather Thunderbird over Outlook because it's open source.
Positive comment•
0

St YUDA
It can access email server just as outlook
Positive comment•
1

Show more comments ▾
5 of 14 comments
K-9 Mail
Is this is a good alternative?
Yes
No
Free • Open Source
Email Client
Android
Android Tablet
F-Droid
46 K-9 Mail alternatives
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 is the most popular Android & Android Tablet alternative to Microsoft Office Outlook.
Suggest and vote on features
K-9 Mail Features
1. Ad-freeK-9 Mail doesn't contain any form of external advertising.
2. Multiple Account supportK-9 Mail support multiple accounts without the need to logout and login
3. Privacy focusedK-9 Mail is considered a privacy friendly alternative.
4. PGP EncryptionK-9 Mail supports PGP, an encryption system used for sending encrypted emails and files.
5. End-to-End EncryptionK-9 Mail has E2E Encryption, for entire or parts of the app.
6. No TrackingK-9 Mail will not track you or use your personal data.
7. Unified inboxView e-mails (or similar) from all accounts in one unified view with K-9 Mail.
8. Works OfflineK-9 Mail can be used without the need to connect to the internet.
9. LightweightK-9 Mail consumes less device resources compared to similar apps.
IMAP Support
Configurable
POP3 Support
One view multiple accounts
Contacts
Exchange
Custom notifications
Header sorting
Comments about K-9 Mail as a Alternative to Microsoft Office Outlook
Most users think K-9 Mail is a great Microsoft Office Outlook alternative.
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•
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•
1
Evolution
Is this is a good alternative?
Yes
No
Free • Open Source
Email Client
Calendar App
Linux
BSD
Flathub
S/MIME
GNOME
OpenPGP
83 Evolution alternatives
Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality. Evolution supports a wide range of industry standard data formats and network protocols for information exchange, with an emphasis on...
Suggest and vote on features
Evolution Features
1. Calendar IntegrationEvolution lets you sync your tasks and events with your calendar application.
2. Calendar ViewEvolution has a built-in calendar view to have a clear overview of your content over time.
3. Ad-freeEvolution doesn't contain any form of external advertising.
4. Multiple Account supportEvolution support multiple accounts without the need to logout and login
5. GPG EncryptionEvolution supports GPG (aka GnuPG) for encryption of things like emails, messages, files, etc.
6. Spam FilterEvolution can detect unsolicited, unwanted and virus-infected emails, calls, files, etc.
7. RemindersEvolution allows you to set reminders for tasks, events or actions, based on parameters of time, place or condition.
8. Sync with Google CalendarEvolution can be synchronized with Google Calendar
Contacts
CalDAV Support
Encrypted Email
CardDAV Support
Personal Information Manager (PIM)
IMAP Support
Exchange
POP3 Support
Multiple languages
Integrated Spam Protection
Comments about Evolution as a Alternative to Microsoft Office Outlook
Most users think Evolution is a great Microsoft Office Outlook alternative.
Guest
It runs on Linux and you still have content if you are offline.
Top positive comment•
1

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•
1

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•
-1

Guest
I've found it better than thunderbird and it can work with exchange just with one free plugin
Positive comment•
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•
1
Mailspring
Is this is a good alternative?
Yes
No
Freemium • Open Source
Email Client
Mac
Windows
Linux
Arch Linux
Fedora
Ubuntu
45 Mailspring alternatives
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.
Suggest and vote on features
Mailspring Features
1. Unified inboxView e-mails (or similar) from all accounts in one unified view with Mailspring.
2. Multiple Account supportMailspring support multiple accounts without the need to logout and login
3. Dark ModeMailspring supports dark mode for comfortable usage in low light conditions.
4. Support for ThemesYou can use themes and templates to change the look and feel of Mailspring.
5. Ad-freeMailspring doesn't contain any form of external advertising.
6. Email OrganizerMailspring allows you to take control of your inbox by filtering and control tools.
7. Extensible by Plugins/ExtensionsMailspring can be extended with add-ons, plugins and extensions.
Customizable
Email tracking
User friendly
Snooze Mail
Built-in translation
Built-in themes
Auto Update
Notifications
Sidebar
Theme Customization
Comments about Mailspring as a Alternative to Microsoft Office Outlook
Most users think Mailspring is a great Microsoft Office Outlook alternative.
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•
0

Guest
Speed of work, good connection to the mail server, speed search.
Positive comment•
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•
0
FairEmail
Is this is a good alternative?
Yes
No
Freemium • Open Source
Email Client
Android
Android Tablet
F-Droid
46 FairEmail alternatives
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.
Suggest and vote on features
FairEmail Features
1. Privacy focusedFairEmail is considered a privacy friendly alternative.
2. Multiple Account supportFairEmail support multiple accounts without the need to logout and login
3. PGP EncryptionFairEmail supports PGP, an encryption system used for sending encrypted emails and files.
4. Block TrackersFairEmail has a feature to block trackers from tracking you.
5. Works OfflineFairEmail can be used without the need to connect to the internet.
6. Ad-freeFairEmail doesn't contain any form of external advertising.
7. No TrackingFairEmail will not track you or use your personal data.
8. Calendar IntegrationFairEmail lets you sync your tasks and events with your calendar application.
Customizable
Email notifications
Extensive settings menu
IMAP Support
Notifications
S/MIME Support
Comments about FairEmail as a Alternative to Microsoft Office Outlook
pros, cons and recent comments
Rasheed
open source, secure, regularly updated
Positive comment•
1
Geary
Is this is a good alternative?
Yes
No
Free • Open Source
Email Client
Linux
BSD
Flathub
GNOME
Flatpak
52 Geary alternatives
Geary is an email application built around conversations, for the GNOME 3 desktop.
Suggest and vote on features
Geary Features
1. Multiple Account supportGeary support multiple accounts without the need to logout and login
2. Dark ModeGeary supports dark mode for comfortable usage in low light conditions.
3. LightweightGeary consumes less device resources compared to similar apps.
4. Spam FilterGeary can detect unsolicited, unwanted and virus-infected emails, calls, files, etc.
5. Ad-freeGeary doesn't contain any form of external advertising.
6. Privacy focusedGeary is considered a privacy friendly alternative.
7. Email OrganizerGeary allows you to take control of your inbox by filtering and control tools.
Conversational email approach
SMTP Support
IMAP Support
Labels for content
Gmail integration
Multiple languages
Comments about Geary as a Alternative to Microsoft Office Outlook
Most users think Geary is a great Microsoft Office Outlook alternative.
Guest
Beatiful frontend Stable working Advanced features
Positive comment•
1
Claws Mail
Is this is a good alternative?
Yes
No
Free • Open Source
Email Client
Calendar App
Windows
Linux
BSD
84 Claws Mail alternatives
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.
Suggest and vote on features
Claws Mail Features
1. LightweightClaws Mail consumes less device resources compared to similar apps.
2. Extensible by Plugins/ExtensionsClaws Mail can be extended with add-ons, plugins and extensions.
3. Multiple Account supportClaws Mail support multiple accounts without the need to logout and login
4. No registration requiredYou can use most of the features in Claws Mail without registration.
5. Spam FilterClaws Mail can detect unsolicited, unwanted and virus-infected emails, calls, files, etc.
6. Privacy focusedClaws Mail is considered a privacy friendly alternative.
7. Works OfflineClaws Mail can be used without the need to connect to the internet.
8. Calendar IntegrationClaws Mail lets you sync your tasks and events with your calendar application.
9. PortableClaws Mail can be used from a USB stick or similar with no prior installation.
IMAP Support
Customizable
Ad-free
GPG Encryption
Import/Export OPML Feeds
End-to-End Encryption
Built-in RSS reader
Integrated Email Client
Multiple languages
Content Filtering
Comments about Claws Mail as a Alternative to Microsoft Office Outlook
Some users think Claws Mail is a great Microsoft Office Outlook alternative, some don't.
Guest
Claws Mail is email only, does not have many of the features of Outlook. Displaying HTML mail is sketchy at best.
Negative comment•
-2