Mailspring is an open source email client for Mac, Windows, and Linux. It offers powerful features to help you manage your inbox, including a unified view of all your accounts, smarter search, snooze and follow-up reminders, and an integrated calendar to help you stay organized. With Mailspring's powerful search capabilities, you can quickly find emails and contacts, and easily create and manage filters to keep your inbox organized. The built-in calendar helps you stay on top of events and meetings, and you can use Mailspring to connect to popular services like Dropbox, Evernote, and Google Drive. You can also set up custom integrations to keep track of your tasks and notifications.
Discontinued On its github page, it indicates that it is archived and no longer maintained.