How to configure postfix to bcc an email as an attachment?

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http://serverfault.com – I can configure postfix with e.g. recipient_bcc_maps to copy sender or recipient emails to an address. However what I need is to not just forward a copy of the original mail, but rather to compose a new blank email from the original sender/recipient and attach the original email as a .eml attachment. The destination is a 'dropbox' for a webapp and requires the email be forwarded as an attachment. What's a simple way to achieve this on Linux ? (HowTos)