Whenever a message is sent or received, a certain method (or function) in your program will be called, passing you the name of a file which contains the message in its entirety in MIME format. You may do anything within this function, including deleting this file, moving it to another user, or mailing it externally. What you return from this function determines whether or not WorkgroupMail sends the message to the message quarantine.
When your plug-in is imported into the WorkgroupMail administrator, it will be visible as an entry in the left-hand list. When a user double clicks on the plug-in entry, another function will be called in your program, enabling you to show whatever user interface you wish. This may be anything from a message box, to a multi-page property sheet to a full blown application.
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