Sparrow was discontinued by Google, but don't worry we have compiled a list of Sparrow Alternatives:
Geary is an email application built for GNOME 3.
Airmail is a lightweight and lightning fast mail client for Mac.
Mutt is a small but very powerful text-based mail client for Unix operating systems.
Mail and Calendar apps already built in Windows 10.
Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).
Email client by KDE, supporting POP3 and IMAP mailboxes.
Part of the Microsoft Office Suite, Outlook is a personal information manager that lets you manage your e-mail, calendar, contacts, and tasks.
eM Client is a full featured e-mail client with a modern and easy to use interface. eM Client also offers calendar, tasks, contacts and chat.
E-mail app with all the great features: swipes (long/short), snooze, add (multiple) attachments.
Mailbird is a Windows based email client which design and style match Windows 7, 8 and XP’s native styles. Mailbird provides clean, simple and lightning fast email experience.
Apple Mail changes the way you interact with your email every day.
Postbox is an email application that helps you organize your work life and get stuff done.