Mailspring vs Mozilla Thunderbird

Mailspring is a desktop email client for Linux, macOS, and Windows, with support for multiple accounts in one inbox. It connects to Gmail, iCloud, Office 365, Fastmail, Outlook.com, Yahoo!, and IMAP/SMTP providers, and indexes email for advanced Gmail-style searches across connected accounts. The client works offline and supports scheduled sending. Its free features include undo send, spell and grammar checking, custom themes, dark mode, and localization. Pro adds read receipts, link tracking, send later, follow-up reminders, templates, contact profiles, snoozing, and mailbox insights. Mailspring connects to mail providers through IMAP and to calendars and contacts through CalDAV and CardDAV, though calendar tools are not included in the app. It can translate drafts into Spanish, Russian, simplified Chinese, French, and German, and offer to translate incoming messages. Mailspring says credentials are kept in the system keychain and email is not processed in the cloud. The free plan is available; Pro costs $8 a month, billed monthly.

Mozilla Thunderbird is a free, open-source email application for Windows, Linux, macOS, and Android. Users can manage multiple accounts separately or combine them in a unified inbox. The app includes calendar, contacts, and task tools; desktop users can also work offline and schedule messages. Its interface is customizable, and it supports third-party add-ons. Thunderbird says it does not put ads in the inbox or sell inbox advertising, and that user donations fund the project. It describes privacy and security as priorities and says its open-source code has been reviewed and improved over 20 years. The application is part of MZLA Technologies Corporation, owned by Mozilla.org. Help and getting-started resources are available for desktop and mobile users, with contributors around the world supporting the project. Thunderbird is available free forever, with donations optional; its listed mobile platform is Android.