/*Check mail address string entered in field*/
function checkmailaddress(str) {
/* define global variables*/
    var at="@"
    var dot="."
    var lat=str.indexOf(at)
    var lstr=str.length
    var ldot=str.indexOf(dot)
	
	/*find the first occurrence of an invalid string input*/
    if (str.indexOf(at)==-1){
       alert("This is NOT a invalid E-mail address!")
       //String is not valid
	   return false
    }
	/*find the first occurrence of an invalid string input*/
    if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){
       alert("To process this form a valid email address is mandatory. A valid email address looks like this ' billme@yahoo.com '. Please try again!")
      //String is not valid 
	   return false
	  }

    if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){
        alert("To process this form a valid email address is mandatory. A valid email address looks like this ' billme@yahoo.com '. Please try again!")
		//String is not valid
        return false
    }

     if (str.indexOf(at,(lat+1))!=-1){
        alert("To process this form a valid email address is mandatory. A valid email address looks like this ' billme@yahoo.com '. Please try again!")
		//String is not valid
        return false
     }

     if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){
        alert("To process this form a valid email address is mandatory. A valid email address looks like this ' billme@yahoo.com '. Please try again!")
		//String is not valid
	   	return false
     }

     if (str.indexOf(dot,(lat+2))==-1){
        alert("To process this form a valid email address is mandatory. A valid email address looks like this ' billme@yahoo.com '. Please try again!")
        //String is not valid
		return false
     }
    
     if (str.indexOf(" ")!=-1){
        alert("To process this form a valid email address is mandatory. A valid email address looks like this ' billme@yahoo.com '. Please try again!")
		//String is not valid
        return false
     }
	//Otherwise string is valid
     return true          
  }

<!-- ================= JavaScript Function ValidateForm validates input of EmailRemove==================== -->  
function ValidateForm(){
  var mailaddress=document.feedback.txtEmail
  /* Check field value for valid input*/
  if ((mailaddress.value==null)||(mailaddress.value=="")){
    alert("To process this form a valid email address is mandatory. A valid email address looks like this ' billme@yahoo.com '. Please try again!")/* Alert if field has no valid input*/
    mailaddress.focus()/*set focus on mail address field*/
    //String is not valid
	return false
  }
    /*Check for valid mail adress*/
  if (checkmailaddress(mailaddress.value)==false){
    mailaddress.value=""
    mailaddress.focus()  /*Check for valid mail adress*/
	//String is not valid
    return false
  }
  //String is valid
  return true
 }