Today I had an issue that I needed to resend quarantined emails.
You can simply execute the following command to inject the mails to postfix


sendmail -t < name_of_the_raw_email_file

Source:
Thanks Wietse (Author of Postfix)
http://postfix.1071664.n5.nabble.com/best-way-to-send-quot-raw-quot-email-files-td45960.html