Thunderbird Plugin: automatically send mails to backup account

Hello, we are little company with 50 users, 3rd party mail provider with IMAP and Thunderbird client on local PCs to manage emails. We need Mozilla plugin that will send a copy of all outgoing messages to a backup account. Our users should not be able to see that, so the built-in hidden copy isn't sufficient. Main reason is creating backup and log - we need to monitor that nobody is sending confidential data out of company.