Default Account Creation and Assignment
When a new contact is automatically created and there is no existing account with a website URL that matches the new contact's email address, the new contact will automatically be assigned to a specified default account. For example, if a contact with an email address firstname.lastname@example.org is automatically created, E2CP will try to match example.com against the standard website field on all account records. If http://www.example.com does not exist, then the new contact will be assigned to the specified default account.
If you enable Auto Add New Contacts, then you must have a "default account." The default account is required because 'orphaned' contacts are private and cannot be seen by other users or included in reports. You can check this default account periodically and run reports on these contacts to manually associate them with real accounts.
Step 1 - Create an account, for example "Support Contacts to Reassign"
Step 2 - Navigate to the Settings tab of the Email to Case Premium app, click the picklist on the right that reads Jump to and choose Inbound Configuration. At the bottom of the page, enter "Support Contacts to Reassign" as pictured below.