Copying emails from a specific domain

Is it possible to configure sendmail to COPY emails sent from a specific domain to another email address? We have a marketing guy (john) who is on the road alot, and a client is concerned that someone should respond asap to their email, even though he is out of the office. Example is: email addressed to john@myoffice.net from whoever@client.com should also copy to me@myoffice.net.
I don’t want all emails addressed to john, just those from the @client.com domain. Any ideas on this would be appreciated.
Thanks