The best alternative to Mailspring is Betterbird, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to Mailspring and seven of them are so hopefully you can find a suitable replacement. Other interesting alternatives to Mailspring are FairEmail, eM Client, KMail and Airmail.
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.
Open-source, privacy-focused email client offering features such as encryption via OpenPGP and S/MIME, unlimited accounts, a unified inbox, customizable settings, and reformatted emails to prevent phishing. Supports two-way synchronization and provides Pro features for additional customization.
eM Client is a full featured e-mail client with a modern and easy to use interface. eM Client also offers calendar, tasks, contacts, notes and chat.
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.
Engineered for iOS, macOS, and watchOS, this fast mail client supports multiple account types, custom actions, Smart Inbox filtering, unified inbox, privacy mode, email scheduling, snooze, third-party app integration, flexible personalization, and advanced workflow tools.
Germany
EU
Netherlands
Czechia
Italy
emClient is wonderful for power users who like to change fonts and styles. However, I cannot swipe on mac. Swipe only works for Windows.