Express Mail is a very simple addon, it allows for quick opening of mail by shift-clicking in your inbox. On shift-click it will take any cash and items, or delete an entry if it only contains text. EM will never accept COD items, you must do this manually.
Express Mail is not showing up as an addon in the initial addon list at the character selection menu. it is installed the same way as all my other addons. not even listed as disabled or incompatible, just not present