Works with K 9 - mkulicke/k-9 GitHub Wiki

Many other Android applications build on K-9's functionality. Searching for K-9 in the Android market will turn up lots of things; here are some of the more useful-looking ones. Please feel free to add longer descriptions.

Security / Encryption:

• APG - GPG Email Encryption for Android
• X509Tools

Widgets:

• Email Widget - Fancy mail preview and count widgets (paid)
• K-9 Data Killer - Allows you to manage background sync
• MailListWidget for K-9 - Mail list preview widget
• K-9 Mail DashClock Extension - An extension for DashClock Widget to display the number of unread messages in K-9 Mail

Notification:

• SMS, my Car and Me - Reads out received emails
• Email Popup - Popup dialog notification on incoming message
• MetaWatch Community Edition - Displays received emails on the watch screen, along with an unread count widget
• K-9 Mail for SmartWatch