Google Inbox vs K-9

Inbox follows Google's Material Design guidelines, making for an intuitive and smart looking interface. Bold colors with clear text and intuitive actions allow for one of the better looking in house Google apps on Android.

Inbox tries automatically bundling similar messages together. For example, Inbox will create bundles for travel information, receipts, promotions as well as group messages temporally. It enables also managing these bundles of messages together - they can all be swiped away together.

It's possible to "hide" a message until a specific date and time or location, which gets the message out of your way until you're ready to deal with it. Swipe left and you can have the email disappear for a day, a week, a month, etc.

Inbox has intuitive swipe gestures that allow quickly dealing with emails or groups of emails. It's possible to mark them done, archive them or snooze them for later by swiping. It allows you to keep inbox at zero messages easily.

If an email contains pictures, flight information, reservation at a restaurant, attachments, links, dates, phone numbers and other information that the application recognizes, it will surface that information in its main view. These items can be viewed and interacted with without having to open the message itself. It allows finding and taking action on the important email information quickly.

You are able to add notes or reminders to pinned items - very useful for long email chains when you can't remember what the main point was!

For users of Google Now, Inbox integrates with the service allowing for reminders to be seen while using Google Now as well as set through the service.

Through a feature called Assists, Inbox offers context sensitive updates to messages. These include information such as flight status updates before a scheduled flight.

If a message includes a date, Inbox is capable of automatically creating a task from that information.

Can reply to emails using an AI generated response

Centralized "folder" for trip info such as airline, hotel, and rental car reservations. Similar to Google Trips.

In addition to the several automatic categories, you can also create your own bundles. Thus reduces clutter and enables you to archive a whole bunch of mails with one swipe.

K-9 is available for free and licensed under the Apache License version 2.0 with source code available here.

K-9 mail does not use too many system resources when using the app, which allow it to be fast and lightweight.

It's possible to complete encrypt email communications via PGP using K-9.

Works well with locally maintained IMAP server.

On a tablet the UI looks a little different but given the extra real estate is logical.
Options to enable UI widgets a plus, can be enabled on a tablet and disabled on a phone.

There is a fork of K-9 available on Google Play that uses Material design, improves the interface a lot.

Threaded email support is better than most.