Outlook Express API - a framework for developing Outlook Express plugins and smooth integration with custom applications.
It supports adding new toolbars to main window and to compose email window. Message store interfaces allows accessing individual emails, folders and account information. API allows interacting with a user by sending various notification events to a custom plugin, including message and folder selection change notifications, new message receiving, folder creation, renaming and deletion, new compose window popup.
OEAPI also supports outgoing email interception and modification. Outgoing email can be cancelled.