function emailcheck (emailStr) {

// Rutina de javascript que valida un email
var knownDomsPat=/^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum|ve|es|tv|cat)$/;
var emailPat=/^(.+)@(.+)$/;
var specialChars="\\(\\)><@,;:\\\\\\\"\\.\\[\\]";
var validChars="\[^\\s" + specialChars + "\]";
var quotedUser="(\"[^\"]*\")";
var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/;
var atom=validChars + '+';
var word="(" + atom + "|" + quotedUser + ")";
var userPat=new RegExp("^" + word + "(\\." + word + ")*$");
var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$");
var matchArray=emailStr.match(emailPat);
if (emailStr=="") return true;  // Se admite que el email venga en blanco
if (matchArray==null) {alert('');return false;}
var user=matchArray[1];
var domain=matchArray[2];
for (i=0; i<user.length; i++) {if (user.charCodeAt(i)>127) {alert('');return false;}}
for (i=0; i<domain.length; i++) {if (domain.charCodeAt(i)>127) {alert('');return false;}}
if (user.match(userPat)==null) {alert('');return false;}
var IPArray=domain.match(ipDomainPat);
if (IPArray!=null) {
	for (var i=1;i<=4;i++) {if (IPArray[i]>255) {alert('');return false;}}
	return true;
}
var atomPat=new RegExp("^" + atom + "$");
var domArr=domain.split(".");
var len=domArr.length;
for (i=0;i<len;i++) {
	if (domArr[i].search(atomPat)==-1) {alert('');return false;}
}
if (domArr[domArr.length-1].length!=2 && 
domArr[domArr.length-1].search(knownDomsPat)==-1) {alert('');return false;}
if (len<2) {alert('');return false;}
return true;
}