Alternatives to Mailspring for Linux with any license

Thunderbird

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

Free Open Source Mac Windows Linux BSD PortableApps.com ... Haiku
Extensible by Plugins/Extensions Built-in RSS reader Calendar integration Support for IMAP ... Multiple Account support Open Source apps SMTP integration Add-ons Built-in Calendar Categories Customizable Delivery reports Encryption Extensible by Plugins/Extensions Free API Gmail integration Google Calendar integration Import from Google Reader HTML Compose Integrated Chat Integrated Password Manager Integrated Web Browser Legacy addons support Open source software Export to OPML Import feeds from OPML Protected by Password POP3 Support Portable Secure File Sharing Tabbed interface Support for Themes Add a feature

1920 Like
Evolution

Evolution is the official personal information manager and workgroup information management tool for GNOME. It combines e-mail, calendar, address book, and task list...

Free Open Source Linux BSD S/MIME GNOME OpenPGP
Calendar integration CalDAV Built-in RSS reader CardDAV ... Encrypted Email Integrated Spam Protection Multiple languages POP3 Support Add a feature

164 Like
Geary

Geary is an email application built for GNOME 3. It allows you to read and send email with a simple, modern interface.

Free Open Source Linux Chrome OS BSD GNOME
Multiple Account support Add a feature

77 Like
Kontact - KMail

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...

Free Open Source Mac Windows Linux BSD
No features added Add a feature

36 Like
Shift

Shift is an email client that makes navigating between Mail, Calendar, Drive + your favorite Apps & Extensions easy (for Gmail, Outlook.com - Office 365 &...

Freemium $ $ $ Mac Windows Linux
Unified search Multiple Account support Android Sync Cross account search ... Extensions Gmail integration Google Apps integration Apps that Sync with Google Calendar Google Drive integration Sync with Google Drive GSuite Integration Multiple Account support Outlook integration Salesforce integration Add a feature

26 Like
Wavebox

Bringing the Gmail & Google Inbox experience to your desktop in a neatly packaged app .

Freemium $ $ $ Open Source Mac Windows Linux
Gmail integration Support for Keyboard Shortcuts Add a feature

13 Like
Pantheon Mail

Pantheon Mail is a free open source email client forked by the elementary OS community from Geary...

Free Open Source Linux elementary OS
Multiple Account support Add a feature

8 Like
Zimbra Desktop

The free Zimbra Desktop client allows you to meld the online and offline worlds – storing and synching your email, calendar, contacts, files and documents in the cloud...
- Discontinued From download page: "The Zimbra Desktop is no longer supported. It will reach the end of Technical Guidance October 1, 2019.". See https://www.zimbra.com/downloads/zimbra-desktop/
Free Personal Mac Windows Linux
No features added Add a feature

30 Like
Nylas Mail Lives

Nylas Mail Lives is a fork of Nylas Mail that fixes many longstanding issues, improves the client experience, and is committed to...
- Discontinued On its github page it states it is archived and is no longer maintained.
Free Open Source Mac Windows Linux Self-Hosted
Extensible by Plugins/Extensions Multiple Account support Add a feature

3 Like
Hiri

Fast, good looking email client. Lighter than MS Outlook with some unique and clever features. Works ONLY with Outlook / Exchange.

Commercial $ $ $ Mac Windows Linux
Calendar integration Office 365 integration Convert Email to Task Add a feature

31 Like
Kube

Kube is a modern communication and collaboration client built with QtQuick on top of a high performance, low resource usage core. It provides online and offline access...

Free Open Source Linux
No features added Add a feature

4 Like