If i'm getting your question right you have a datatable in the viewstate and you want to add all the values from rows of a particular column to the list you have shown above. if that is the case you can:
1- Get Datatable from viewstate.
DataTable dataTable = ViewState["myDataTable"]
2- Get the list from GetEmployeeList(...).
List<Employee> listEmployee = GetEmployeeList();
3- Iterate through rows of datatable and add values to your list variable.
for(rowIndex=0; rowIndex<datatable.rows.count;>{
string columnValue = dataTable.Rows[rowIndex]["email"];
Employee emp = new Employee(){ID=someID, Email=columnValue});
}
Hope it will help.
thanks,
Hemant