Open up the users mail file, go to create - Agent
Once faced with the box, you are faced with a list of conditions etc.
To forward mail from one users mail file to anothers, simply enter the following:
When should this agent run: After new mail has arrived
Which documents should it act on? This will be set to - Newly received mail documents
You can then add conditions for this so it will only forward certain emails (i.e. from certain people/ certain subject etc) - to do this select Add Search
To forward the mail with the applied conditions, select Add Action from the bottom left corner. Whemn the box pops up, change the Action to Send Mail Message. Enter the name in the address box and also any subject you wish. You can even enter some text if you wish, like 'Here's A's emails. Check the box, include copy of document then save and close.
If this is set up on a server, it may take a while for it to kick in, but it should be ok. As with most things, you can disable this by going to View - Agents and deselecting it.
Saying all that, why do you need to forward on mail, when you can just add people to his ACL with reader access?
John