Force a Blind Carbon Copy ?

We are in need of a way to send email from one particular user to a 3rd party for email retention. Specifically, all messages composed from this user need to be copied to an external email address and sent to a data retention site.

I am thinking it would be possible to force a blind carbon copy to this external email address each time this user composes a new message.

Is it possible to do this without getting the user involved or even giving the user an option to delete or disable this BCC? or is there a different way somewhere in Exchange that could allow a copy of all messages be sent to a different user? Thx for any suggestion.