If this is an exchange account then have him add you to the permissions of his mailbox. To do this he right-clicks on Mailbox-(his name here) at the very top of the folder list and adds your permissions to that level. Then you can add his mailbox to your folder list. Go to tools, account settings, click change, click more settings, click the advanced tab and add his mailbox there. To work in his mailbox as though you are at his computer and have full control you need to create a new profile. First go to the control panel and open the mail icon, click show profiles and change the selection to prompt for a profile. Close and re-open outlook and you will get prompted for a profile. Click "new" and create a profile for your boss's mailbox. Once created you can choose to open his profile or yours whenever you open outlook.

If this is an exchange account then have him add you to the permissions of his mailbox. To do this he right-clicks on Mailbox-(his name here) at the very top of the folder list and adds your permissions to that level. Then you can add his mailbox to your folder list. Go to tools, account settings, click change, click more settings, click the advanced tab and add his mailbox there. To work in his mailbox as though you are at his computer and have full control you need to create a new profile. First go to the control panel and open the mail icon, click show profiles and change the selection to prompt for a profile. Close and re-open outlook and you will get prompted for a profile. Click "new" and create a profile for your boss's mailbox. Once created you can choose to open his profile or yours whenever you open outlook.