I'll suggest one of the most successful devices that is quick convert PST File into MBOX and that knows as eSoftTools PST to MBOX Converter Software. It works quickly and straightforwardly. Every folder in a PST file should be exported as a separate MBOX file. Supports a variety of email clients, including Thunderbird, Eudora, Mulberry, and others. The device can convert PST File to Thunderbird forward with all mailbox item such as - emails, contacts, calendar, attachments, task, notes and other. For the whole consumer, a free trial version is available.