function isEmailString (InString) {
//Function to test if student email has only one @ character, and made of digits/chars/./_ only (no slashes)
   if(InString.length==0) return (true);
   var RefString="01234567890abcdefghijklmnopqrstuvwxyz_.@";
   var atSign="@";
   var valid=0;
   var atCount=0;
   InString=InString.toLowerCase();

   for (Count=0; Count < InString.length; Count++) {
      if (valid==0)
         {TempChar= InString.substring (Count, Count+1);
         if (RefString.indexOf(TempChar,0)!=-1)
            {valid=0;
            if (TempChar=="@")
               {atCount++;}}//End of if atString statement
         else
            {valid=1;} //End of if refstring statement
         }//End of if valid=0
   }//End of for loop

   if (atCount !=1){valid=1;} 
   return (valid);

} //End of function