When comparing Google Inbox vs Yahoo! Mail, the Slant community recommends Google Inbox for most people. In the question“What are the best e-mail clients for Android? ” Google Inbox is ranked 6th while Yahoo! Mail is ranked 24th. The most important reason people chose Google Inbox is:
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.
Specs
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Pros

Pro Good-looking interface
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.
Pro Intelligent categorization
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.
Pro Can snooze emails
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.

Pro Helps deal with messages quickly
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.
Pro Surfaces important information from messages
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.
Pro Can add notes to emails
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!
Pro Integrates Google Now reminders
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.
Pro Integrates realtime updates in messages
Through a feature called Assists, Inbox offers context sensitive updates to messages. These include information such as flight status updates before a scheduled flight.
Pro Can create tasks from dates and tasks in messages
If a message includes a date, Inbox is capable of automatically creating a task from that information.
Pro Auto replies
Can reply to emails using an AI generated response
Pro Trips Bundle
Centralized "folder" for trip info such as airline, hotel, and rental car reservations. Similar to Google Trips.
Pro Categorizes mails by Bundles
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.
Pro Tabs
With this Yahoo! Mail feature users can open any e-mail in a new tab and get back to the mail list without having to close the e-mail that the user is currently reading.
Pro Background wallpaper
Similar to Mail app bundled in Windows 10, Yahoo! Mail allows users to set images from Flickr as the background image for the app.
Pro Stationary
Stationary is an add-on that's only available in Yahoo! Mail. It allows users to customize and enhance the look of the email. Things like image borders, letter style etc. can be changed before sending the email to intended recipients.
Cons

Con Only supports Gmail accounts
No exchange email support or importing of any other e-mail services mail.
Con Will be shut down in March 2019
Con No rich-text (HTML) formatting for composing mails
Con No way to mark a message as unread once it's read
Con No way to delete a single message in a bundle
