You can easily convert MacUncle OST files using MacUncle OST Attachemnt Extractor. The tool supports Mac OS Machines.
Start MacUncle OST Attachment Extractor on your Mac Machine
Use Add File(s) or Add Folder(s) to upload OST files to the software panel.
Click on the required Email message to extract attachment.
Press Extract from the top menu and browse destination location and set the Filter option field.
Hit Start Extract to initiate the process of Attachment extraction
Get the extracted OST attachments in the selected location.