If you have configured your enterprise server to use an external security manager, and you are not using casesm, the Users button on the left sidebar of the ESMAC interface is removed. Where you are using casesm, the Users button is only displayed if you have set the Local security enabled option on the mfuser SNT definition.
To enable legacy security when you are not using casesm or any other external security manager, you set the Local security enabled option on the mfuser SNT definition. This option has no influence on behaviour when you are using an external security manager other than casesm.
For instructions on enabling legacy security, with and without casesm, and for instructions on setting the Local security enabled option, see To use legacy Enterprise Server MSS Security.