Manual Method to Convert PST to MBOX -
Go to your Outlook account.
Select File >> Open and import >> ImportExportTools.
Now, choose the export a file.
Choose Personal Folder File (.PST) and click Next.
Select the items that you want to transfer.
Set the destination for the file.
Now, go to your Mac system and open Outlook.
Select File >> Import >> Personal Folder File (.PST) >> Next.
Here, choose Outlook for Windows Data File(.PST) and proceed.
Select the location of the earlier saved PST file and hit on Import.
Here, all the migrated PST files will be stored in the Outlook folder.
Now, drag the folder into your desktop.
Hope This Works,
Peter