When submitting feedback with email notificatins enabled, the following exception is thrown:

Coding error detected, it must be fixed by a programmer: Could not load preference message_provider_mod_feedback_loggedoff. Does the component and name you supplied to message_send() match a row in message_providers? Message providers must appear in the database so users can configure how they will be notified when they receive messages.

The problem appears to be that the plugin is not declaring its message providers or using send_message() correctly.

1) need to have a mod/feedback/db/messages.php which a message provider
2) the message_send() calls in mod/feedback/lib.php need to have component set to "mod_feedback" and name set to the provider name declared in messages.php

mod/quiz/ and mod/forum/ appear to provide good examples of this.