K-9 Mail - K-9 is an opensource email client making it easy to chew through large volumes of email.
Spark Mail - 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
FairEmail - Open source, privacy friendly email app
MailTamer - Don’t get buried in mountains of emails and let them get control of you and your inbox again!
Evolution - Apps/Evolution - GNOME Wiki!
Express Mail - Best mobile email app for Salespeople