When comparing Newton Mail vs K-9, the Slant community recommends K-9 for most people. In the question“What are the best e-mail clients for Android? ” K-9 is ranked 2nd while Newton Mail is ranked 11th.
Ranked in these QuestionsQuestion Ranking
Pro Multi-account support
Gmail, Yahoo Mail, Outlook, iCloud, Google Apps, OWA, Microsoft Exchange, Office 365, AOL and other IMAP accounts.
Pro Synchronizes settings across devices
CloudMagic saves settings in the cloud. When you switch devices, the app simply pulls your setting from the cloud.
Pro Beautiful, clean design
Intuitive, easy to use user interface.
Pro Unified inbox
Option to view one inbox for all your email accounts.
Pro Emails can be downloaded locally on a per-folder basis
A feature called "sync" allows downloading emails locally on a per-folder basis. That will allow accessing them while offline, keep them always up to date, provide faster search, show unread email count and show push notifications as soon as new messages in those folders pop up.
Pro The app can be locked
It's possible to lock the app behind a four digit passcode.
Pro Helps deal with emails quickly
It's possible to archive, delete or mark emails as read from the notification tray or with swipe gestures.
Pro Android Wear support
Cloud Magic supports sending notifications to Android Wear devices, allowing the user to easily see their mail without having to take their phone out.
Pro Can snooze emails
It's possible to "hide" a message for a set amount of time, which gets the message out of your way until you're ready to deal with it.
Pro Email tracking
Get notified when the recipient reads the e-mail.
Pro Integrates with other services to extend functionality
CloudMagic has 'cards', that allow quick interactions with other services, like Evernote, MailChimp, Salesforce, Trello, etc. And unlike similar integration, these interactions happen within the app itself.
Pro Great search
The app is capable of searching through all of your email and cloud accounts to find specific information. The results show up as they are typed in.
Pro Free trial
Newton mail offers a 14-day free trial.
Pro No privacy concerns
Pro Free an open source
K-9 is available for free and licensed under the Apache License version 2.0 with source code available here.
Pro Complete PGP encryption
It's possible to complete encrypt email communications via PGP using K-9.
K-9 mail does not use too many system resources when using the app, which allow it to be fast and lightweight.
Works well with locally maintained IMAP server.
Pro Material UI version
There is a fork of K-9 available on Google Play that uses Material design, improves the interface a lot.
Pro Excellent email threading
Threaded email support is better than most.
Pro Optimized for phone and tablet
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.
Con Not free anymore, needs a subscription ( $49.99/yr)
The apps stared as a free app but since some time it's only free for 14 days (trial).
After the trial it needs a subscription which is very expensive with $50/yr comparing the features with other free E-Mail apps
Con Privacy concerns
We then use the authorization provided to download your emails on the cloud and push to your devices. We use AWS servers to store your data: emails and authorization.
Con Noisy UI
The user interface is bland and tries to cram a lot of information on screen, making it unpleasant to use.
Con Emails received as forwarded EML attachments are not natively supported
When you receive an email which was forwarded as an EML attachment, K-9 Mail is not able to open it natively. It opens it using a third-party application registered for this mime-type on the device, if any. The Gmail email client app is able to read the EML attachments, thus you need to have it installed as well (or any other EML capable app).