You can use the Regain PST to MBOX Converter tool to change PST format to MBOX while keeping attachments. This advanced software ensures that all your emails, including attachments, are transferred without losing any data. It maintains the folder structure and metadata very efficiently and provides a smooth conversion from Outlook PST to MBOX. With its very simple user interface, the utility will let you convert an entire PST file or extract selected folders into a single or multiple MBOX files. Now you can enjoy the free trial, where you get to convert up to 30 items per folder.