When setting up if you don't have a centralized "corporate" environment and you have multiple clients you first need to log into the system as the domain admin. Click Settings, choose Advanced Settings and then Message Footer. There you need to check the option "Allow domains to override footer settings" or they won't have the option for "Message Footer" option on their individual domains. Once this is checked and saved each domain can set there own. You can also set a global for all domains from the advanced settings.