You can use the Mailvita Backup for IMAP Tool to create a backup of your IMAP mailboxes to PST. It connects directly to your IMAP account and enables you export emails to PST format without losing any data. Just type up the information for your IMAP server, pick the folders you wish to back up, and choose PST as the export format. The application keeps the structure of folders and attachments, so it's a safe and quick way to back up your whole inbox for usage in Outlook.