K-9 Mail is an email application (app) for Android phones or tablets.K-9 supports multiple mailboxes, each independently configurable. This ability to configure the application makes it great for people who get a lot of email and want to be able to manage it flexibly when you are on the move.
K-9 can connect to email servers using all popular methods, including POP3, IMAP and WebDAV protocols.
Because K-9 is an Open Source project, it makes it easy for other coders to add to the project and increase its security and other features.
One such improvement is the ability to encrypt and decrypt email with the popular and well tested PGP encryption method. This makes K-9 a suitable email application for users and organisations who want to be able to handle email securely and responsibly via mobile devices.
Such users include journalists, human rights workers, other workers who have to protect the data of the clients, staff dealing with medical information of their patients and businesses who need to be careful with their confidential intellectual property.
In an era post-Prism and the Snowden disclosures, organisations and individuals cannot be sure that their data is safe from surveillance of governments agency and a wide network of data analysts working with them. Email encryption can be an important step to prevent your data from falling into the wrong hands. K-9 makes the process relatively easy as you will see in the chapter on Security and Encryption.
About Android and this Guide
Android applications are written to work on many different devices with different sized screens including both tablets and phone.
If you are using an device that doesn't have a Menu key then instead you will see a menu icon with three squares on your navigation bar which will give the same options when touched. We will call this the More Actions icon.
The More Actions icon may also appear at the right hand side of in the action bar of your application.
The Menu Button
Older Android devices will normally have a Menu hardware key.
In this case to access the same options listed under the More Actions icon above press the hardware Menu button instead.
Technical Information about K-9
K-9 Mail started life as a fork from the Android Open Source Project's Mail client program by Jesse Vincent of Best Practical Software.
The screen which welcomes you to K-9 gives us an introduction to some of the features which make some improvements on the stock email client which comes with your Android device.
K-9 can be used together with an app called AGP to encrypt emails. Currently this only works with "inline" encryption rather than the more modern pgp/mime encryption. There is more information about this area in the section on encryption.
Many of these are explained in the course of this manual. Others are listed on the project's wiki pages here - https://github.com/k9mail/k-9/wiki/FeatureList
Getting involved and getting help
You can get involved with the K-9 project in different ways. There is a mailing list here which serves as an all purpose first port of call for support and interaction with and between the community of users and developers.
The project also posts updates on their Google Plus page.