K-9 Mail vs. intheloop.io

K-9 is an opensource email client based on the Email application shipped with the initial release of Android. K-9 is focused on making it easy to chew through large volumes of email.

Loop Email is a simple yet powerful team inbox. It's been built with the familiarity of an email client, so it's easy to set up and use for any teams that are used to handling customer messages via email. It's hard being productive when you spend half your time reading emails, and the other half flipping between platforms to tell your team about said emails. You need a single app that's going to help you move faster and keep everything and everyone on the same page. This is Loop.