K-9邮件客户端(K-9 For Pure)支持普通邮件的pop和imap服务器形式。
iPhone4有单一收件箱的邮件客户端，Android也有，而且也不差，这个K-9 Mail支持普通邮件的pop和imap服务器形式，并且是多邮件帐号支持，多收件箱同步，更强的是，支持push mail。
系统自带多国语言。

Changes in v5.201:
• Fixed crash during database upgrade
• Fixed various minor bugs
Changes in v5.200:
• Added support for PGP/MIME
• Added support for bundled notifications on Android 7+ and Android Wear
• Ask for confirmation on" mark all as read"
• Added support for sub-folders (WebDAV)
• Added support for Server Name Indication
• Disabled support for SSLv3 protocol/ciphers and all RC4 ciphers
• Removed support for APG (use OpenKeychain instead)
• Lots of smaller bug fixes and features