Email Archive

I need to archive all Emails (incoming, outgoing - internal, external - everthing) of a certain domain. This should be done by not involving the individual users, but, by the administrator on the domain level.
I have set this up with other sites and mailservers and there, all mails are beeing sent to 1 task-specific mailbox called eg. "archive" without any real user behind it.
How can I accomplish this on my Zoho Biz account, without having to pay for an additional Zoho user? I'd like to send them all to an external mail-address.
Thank you.