function isEmailValid(field) {  
if (field.value.length >0){
i=field.value.indexOf("@");
j=field.value.indexOf(".",i);
k=field.value.indexOf(",");
kk=field.value.indexOf(" ");
jj=field.value.lastIndexOf(".")+1;
len=field.value.length;
if (!((i>0) && (j>(1+1)) && (k==-1) && (kk==-1) &&
(len-jj >=2) && (len-jj<=4))) {
alert("The email address of \""+field.value+"\" appears to be invalid.\nIt should be something like yourname@domain.com\nPlease try again.");
field.focus();
return false;
}
}
return true;
}