K-9 Mail Alternatives

Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!

Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.

The #1 email warming service to improve your deliverability by generating realistic and meaningful engagement to your emails. Easy-to-use solution to help you land in the main inbox instead of the spam folder.

Visit website paid $19.5 / Monthly (Pro)

Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest. Spark for Teams allows you to create, discuss, and share email with your colleagues

Open Source

Mailbird is the best email client for Windows 7, 8 and 10

eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.

freemium

Secure email with absolutely no compromises. Get your free encrypted email account today.

freemium €5.0 / Monthly (user - 5 GB)

Airmail is a lightweight and lightning fast mail client for Mac.

Open source, privacy friendly email app

Open Source

Gmail is available across all your devices Android, iOS, and desktop devices. Sort, collaborate or call a friend without leaving your inbox.

Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.

freemium

Mailspring is a mail client for Mac, Windows and Linux.

Open Source

BlueMail is an email management app for Android, iOS, and Windows.

Apps/Evolution - GNOME Wiki!