The documentation in the Online Help regarding the Field Mapping feature in the article Configure > Setting Up Email > Email Servers > Creating an Inbox is not entirely clear about how the feature is used. It appears to be used to map components from the incoming email to fields on the created object. However, the mappings do not successfully populate fields in the created Incident (or other object) record.
Here is more detail on how the email Field Mapping works:
1. Field Mapping provides values for all the required fields to create or locate a Custom Contact business object (instead of Employee), by unchecking the 'Create or Link to an Employee or External Contact' flag.
2. Once the Incident is created, and this Custom business object is also created or located, it will link to the parent business object (Incident).
3. Field mapping will not alter the values for Incident (parent business object).
4. Field mapping will not alter the values for the Custom Contact business object if it exists, it will only be used to locate (existing) or create (non-existing) the contact record.
5. If the 'Create or Link to an Employee or External Contact' flag is checked, the Field Mapping values will be ignored.