Extracts Mailboxes from Exchange Backup and Saves them in Multiple File Formats. With Stellar Mailbox Extractor for Exchange Backup, you will now be able to get back all your emails that have been stored in the Exchange Backup. The software uses the backup file with .vhdx or .bkf file extensions to extract Offline mailboxes. Key Features: Extracts and Exports offline mailboxes to Live Exchange Server. Extracts mailboxes from corrupt .bkf and .vhdx backup files. Option to save your extracted mailboxes in Office 365 and other file formats. You can look for Specific Emails from the extracted mailboxes. Option to look for backup files in a particular drive or volume. You can preview your mailboxes and their contents.