function check_fields_sendemail() 
{
//if (document.sendemail.txtfrom.value =="")
//{
//alert("Please Enter your email address");
//document.sendemail.txtfrom.focus();
//return(false);
//}
//if(document.sendemail.txtfrom.value!=="")
//{
//	pass=document.sendemail.txtfrom.value.indexOf('@',0);
//	pass1=document.sendemail.txtfrom.value.indexOf('.',0);
//
//	if((pass==-1)||(pass1==-1)) 
//	{
//		alert("Invalid Email Address e.g format : abc@hotmail.com ");
//		document.sendemail.txtfrom.focus();
//		return(false);
//	}
//
//}



<!-- Begin
/* This script and many more are available free online at
The JavaScript Source!! http://javascript.internet.com
Created by: Anita Sudhakar :: http://www.smartwebby.com/DHTML/email_validation.asp */

function echeck(str) {
  var at="@"
  var dot="."
  var lat=str.indexOf(at)
  var lstr=str.length
  var ldot=str.indexOf(dot)
  if (str.indexOf(at)==-1){
     alert("Invalid E-mail address")
     return false
  }
  if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){
     alert("Invalid E-mail address")
     return false
  }
  if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){
     alert("Invalid E-mail address")
      return false
  }
   if (str.indexOf(at,(lat+1))!=-1){
     alert("Invalid E-mail address")
      return false
   }
   if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){
     alert("Invalid E-mail address")
      return false
   }
   if (str.indexOf(dot,(lat+2))==-1){
     alert("Invalid E-mail address")
      return false
   }
   if (str.indexOf(" ")!=-1){
     alert("Invalid E-mail address")
      return false
   }
   return true          
}


  var emailID=document.sendemail.txtfrom
  
  if ((emailID.value==null)||(emailID.value=="")){
    alert("Please Enter your Email ID")
    emailID.focus()
    return false
  }
  if (echeck(emailID.value)==false){
    emailID.value=""
    emailID.focus()
    return false
  }

// End -->



if (document.sendemail.txtmsg.value =="")
{
alert("Please Enter the email meassage");
document.sendemail.txtmsg.focus();
return(false);
}

document.sendemail.submit ();
return(true);
}