The configuration of an instance is broken down into three levels:

• 1) Instance level: The basic settings of an instance such as log behavior or default values are processed at this level. More importantly, however, this is where you define Exchange as the server type and the connection to the mailbox catalog.
• 2) Action tree level: The action tree configurations are evaluated at the level below the instance level. These determine the scope of selection, which is directly related to the settings in the mailbox catalog at the instance level. This is also where you configure the basic filter settings, such as entry points.
• 3) Action level: The action level consists of any number of individual actions that are linked hierarchically. These individual actions represent the actual processing steps. The order of actions in a tree determines the course of processing.

While the configuration is loading, the XML fragments are validated based on the underlying XML schema. This applies both to calling the validation function, which is explicitly limited to checking the syntax of fragments and individual plausibility checks, and at the start of message processing. If the validation of the configuration fails, the mails cannot be processed.