Just type in sys_properties.list into the "Type Filter Text" field and this will bring you to a table of all the system properties. The system property may not exist, although it did for me on my Fuji Patch 3 build (in this case, it's okay to create the system property if it's not already there).
Post fixing a ".list" at the end of a database table name in ServiceNow just brings up the list
Post fixing a ".form" at the end of a database table name in ServiceNow just brings up the form
Sounds like you're still in the implementation phase. I'd highly recommend spending a good deal of time on testing email configs, watermark customizations, etc.
