There were no slaveowners named Mann in Claiborne County, MS in either the 1850 or 1860 Slave census schedules. The nearest Mann listed in a Slave schedule was in neighboring Hinds county in the 1850 census and he was not actually a slaveowner but was actually an overseer, possibly for a C.T. Munis a planter from Virginia. It's pretty complicated stuff and would require quite a lot of research to find if there is a possible connection to your Mann's. Researching slave ancestors is advanced type of research that can take a long time to do and the conventional wisdom is that you need to fully research your family from 1870 to the present before attempting to tackle researching slave ancestors. Good luck.