When comparing Mail Wise 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 7th while Mail Wise is ranked 17th. The most important reason people chose K-9 is:
K-9 is available for free and licensed under the Apache License version 2.0 with source code available [here](https://code.google.com/p/k9mail/).
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Pro Clean threaded conversations
The Enhanced view presents conversations without repetitive information such as signatures.
Pro Requires no additional cloud service
Mail Wise messages aren't routed through an external service. All messages are sent from the server directly to the device.
Pro Can automatically group certain kinds of messages
For example, it's possible to group emails from a single sender together.
Pro Unified inbox
Google, Exchange as well as any IMAP email services are supported by Mail Wise and can be used at the same time from a unified inbox.
Pro Color-coded notifications
Color coding allows for users to set up custom visual ques as to what the notification is for, which makes for a convenient way to glance at ones device to know if the e-mail is something they want to open.
Pro Can snooze notifications
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 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 No privacy concerns
K-9 mail does not use too many system resources when using the app, which allow it to be fast and lightweight.
Pro Complete PGP encryption
It's possible to complete encrypt email communications via PGP using K-9.
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 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.
Pro Excellent email threading
Threaded email support is better than most.
Con Has trouble with Outlook accounts
Con No push notification for anything other than exchange
There is currently no support for push notification for imap accounts, meaning there will be more battery drain due to the constant polling to check for new emails.
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).