Because PST is a proprietary format, it's difficult to find free tools to work with PST. And often the developers that have PST tools have tools to hack/break passwords on them, which makes their products more difficult to trust. (Anyway, that product appears to be from this company: [http://www.stellarinfo.com/email-tools/mbox-to-pst-converter.php]) Are you trying to move mail into Microsoft Outlook? One way is to use an IMAP account as an intermediary. You would upload your messages to the account using Thunderbird, and then download them into Outlook. I'm sure you can find articles with all the details.