Forwarding pop3 sent mail

I have a site that networks with other non-profit agencies and is involved in community projects.

There’s a need for archiving our mail permanently for legal reasons.

I have my panel set to automatically forward a copy of all email ‘inbound’ to the server to an archive mailbox. My users access their mailboxes through Outlook, Windows Mail, etc.

I’ve used dreamhost going on two years, but I can’t determine if or how to retain a copy of outbound mail of my users.

Any advice?