function checkEmail(val){ var emailStr=val; var emailPat=/^(.+)@(.+)$/ var specialChars="\\(\\)<>@,;:\\\\\\\"\\.\\[\\]" var validChars="\[^\\s" + specialChars + "\]" var firstChars=validChars var quotedUser="(\"[^\"]*\")" var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/ var atom="(" + firstChars + validChars + "*" + ")" var word="(" + atom + "|" + quotedUser + ")" // The following pattern describes the structure of the user var userPat=new RegExp("^" + word + "(\\." + word + ")*$") var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$") var matchArray=emailStr.match(emailPat) if (matchArray==null) { alert("The email address you entered is not valid, please verify.") return false; } var user=matchArray[1] var domain=matchArray[2] // See if "user" is valid if (user.match(userPat)==null) { // user is not valid alert("The email address you entered is not valid, please verify.") return false; } var IPArray=domain.match(ipDomainPat) if (IPArray!=null) { // this is an IP address for (var i=1;i<=4;i++) { if (IPArray[i]>255) { alert("The email address you entered is not valid, please verify.") return false; } } } // Domain is symbolic name var domainArray=domain.match(domainPat) if (domainArray==null) { alert("The email address you entered is not valid, please verify.") return false; } var atomPat=new RegExp(atom,"g") var domArr=domain.match(atomPat) var len=domArr.length if (domArr[domArr.length-1].length<2 || domArr[domArr.length-1].length>4) { // the address must end in a two letter or three letter word. alert("Your email address must end in a valid domain extension.") return false; } if (domArr[domArr.length-1].length<=3 && len<2) { var errStr="The email address you entered is not valid, please verify." alert(errStr) return false; } return true; }