You can configure in the Outlook add in the types of Centerbase items you want to be able to attach email to..
Simply navigate to the the add in tab in outlook, and select the Centerbase icon link, shown below
Next, the dialog box will appear. Click on the 'Options' tab. Under the 'Available Link Items' section, check the types of items from your Centerbase database you would like to be able to attach emails to. These will now appear in your 'Attach' list. You can even set which item should be the default item to appear in the attach list, potentially saving you mouse clicks on the item you attach most frequently.