When comparing Aqua Mail vs K-9, the Slant community recommends K-9 for most people. In the question“What are the best Gmail clients for Android?” K-9 is ranked 8th while Aqua Mail is ranked 10th. 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/).
Ranked in these QuestionsQuestion Ranking
Pro Top rated for keeping you info private
Has been rated well on AndroidForumsl.
Pro Integrates with Tasker
Tasker is an automation app. Aqua Mail's Tasker integration allows changing settings, triggering message based events and running mail checks based on criteria like time of day, location, timer, connection type, etc.
Pro Integrates with cloud storage services for backup and restore
It's possible to backup the app along with account settings via services like Dropbox, OneDrive, Box.com, Google Drive.
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.
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.
Con Free version supports only 2 accounts and adds promotional email signature
The base, free application supports up to two accounts and adds a promo signature to all outgoing messages.
Con No support for Exchange Activesync protocol
This is the de facto, secure Exchange over the web protocol used and is enforced by most businesses for enterprise email. Aqua only supports EWS for Exchange, which most enterprise administrators block or disable.
Con Floating ads in free version
It shows floating ads in the email list and they can not be deleted.
Con Limited signature capabilities
Signatures can't have images or HTML.
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).