K-9 Mail really is the grandfather of powerful E-mail apps, but I have switched to Spark a few years back when it became available for Android and never looked

K-9 Mail really is the grandfather of powerful E-mail apps, but I have switched to Spark a few years back when it became available for Android and never looked back. It's just a breeze to use. Sure, I have some gripes with it, but I really like the Google Inbox style of organizing my mail and keeping my inbox tidy.