Native Only'  ports will only present the data in its original format. In this case, the messages are from the Exchange Journal (via Enterprise vault) and will be exported in the envelope format.

Export the messages through the Metadata export.

• Under Options:
  • Select 'Include: msgs in native format and native loose files'
  • Select 'Include Journal Information: By merging recipient lists'
    • If the option to 'Include Journal Information' is grayed out, the case processing settings 'Process journal envelope information' was not selected prior to processing data into the case. This setting cannot be changed after documents are processed.
  • Processing > Settings > Configure processing parameters and features > Process journal envelope information

Note:  Native messages exported through Metadata will be individual MSGs and not contained within a PST.