Foundry376 has launched Mailspring (https://getmailspring.com), a desktop email client designed for macOS High Sierra.
It sports features such as an unified inbox, snoozing, reminders, templates, offline search, and support for Gmail labels. It comes with six built-in themes. The app offers mail rules and customizable keyboard shortcuts.
Mailspring is free and supports all IMAP providers, including Gmail, Office 365 and iCloud. You can swipe to triage mail, see Quicklook thumbnails for attachments, and reply to emails directly from the Notification Center. Mailspring’s email sync has been built from the ground up to use macOS features like App Nap, ensuring it keeps your mailbox up to date without draining your battery, according to the folks at Foundry376.