Using MailtoX desktop it is possible to export email from a PST file and save it as MSG files. 

1. Select
MS Outlook / Exchange from the actions list at the left

2. At the dialog that opens, select
Custom Location (1) and load the PST file by pressing on the dots (2). Press on Load Folders (3) to load the PST folders and then select the folders that you wish to process.

3. Select Outlook MSG from the actions list at the left

4. Select the
Target Folder (1) and select the SubFolders Structure (2)

5. The extract job is ready. Press on
Execute Job to process the files