jQuery function to check email with all popular contraints

gistfile1.js

 function chkmail(emailStr) {
            /* The following variable tells the rest of the function whether or not
            to verify that the address ends in a two-letter country or well-known
            TLD.  1 means check it, 0 means don't. */
            var checkTLD = 1;

            /* The following is the list of known TLDs that an e-mail address must end with. */
            var knownDomsPat = /^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum)$/;

            /* The following pattern is used to check if the entered e-mail address
            fits the user@domain format.  It also is used to separate the username
            from the domain. */
            var emailPat = /^(.+)@@(.+)$/;

            /* The following string represents the pattern for matching all special
            characters.  We don't want to allow special characters in the address. 
            These characters include ( ) < > @@ , ; : \ " . [ ] */
            var specialChars = "\\(\\)><@@,;:\\\\\\\"\\.\\[\\]";

            /* The following string represents the range of characters allowed in a 
            username or domainname.  It really states which chars aren't allowed.*/
            var validChars = "\[^\\s" + specialChars + "\]";

            /* The following pattern applies if the "user" is a quoted string (in
            which case, there are no rules about which characters are allowed
            and which aren't; anything goes).  E.g. "jiminy cricket"@@disney.com
            is a legal e-mail address. */
            var quotedUser = "(\"[^\"]*\")";

            /* The following pattern applies for domains that are IP addresses,
            rather than symbolic names.  E.g. joe@@[123.124.233.4] is a legal
            e-mail address. NOTE: The square brackets are required. */
            var ipDomainPat = /^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/;

            /* The following string represents an atom (basically a series of non-special characters.) */
            var atom = validChars + '+';

            /* The following string represents one word in the typical username.
            For example, in [email protected], john and doe are words.
            Basically, a word is either an atom or quoted string. */
            var word = "(" + atom + "|" + quotedUser + ")";

            // The following pattern describes the structure of the user
            var userPat = new RegExp("^" + word + "(\\." + word + ")*$");

            /* The following pattern describes the structure of a normal symbolic
            domain, as opposed to ipDomainPat, shown above. */
            var domainPat = new RegExp("^" + atom + "(\\." + atom + ")*$");

            /* Finally, let's start trying to figure out if the supplied address is valid. */

            /* Begin with the coarse pattern to simply break up user@domain into
            different pieces that are easy to analyze. */
            var matchArray = emailStr.match(emailPat);
            if (matchArray == null) {
                /* Too many/few 's or something; basically, this address doesn't
                even fit the general mould of a valid e-mail address. */
                //alert("Email address seems incorrect (check  and .'s)");
                return false;
            }
            var user = matchArray[1];
            var domain = matchArray[2];
            // Start by checking that only basic ASCII characters are in the strings (0-127).
            for (i = 0; i < user.length; i++) {
                if (user.charCodeAt(i) > 127) {
                    //alert("Ths username contains invalid characters.");
                    return false;
                }
            }
            for (i = 0; i < domain.length; i++) {
                if (domain.charCodeAt(i) > 127) {
                    //alert("Ths domain name contains invalid characters.");
                    return false;
                }
            }

            // See if "user" is valid 
            if (user.match(userPat) == null) {
                // user is not valid
                //alert("The username doesn't seem to be valid.");
                return false;
            }
            /* if the e-mail address is at an IP address (as opposed to a symbolic
            host name) make sure the IP address is valid. */
            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("Destination IP address is invalid!");
                        return false;
                    }
                }
                return true;
            }

            // Domain is symbolic name.  Check if it's valid.
            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("The domain name does not seem to be valid.");
                    return false;
                }
            }

            /* domain name seems valid, but now make sure that it ends in a
            known top-level domain (like com, edu, gov) or a two-letter word,
            representing country (uk, nl), and that there's a hostname preceding 
            the domain or country. */
            if (checkTLD && domArr[domArr.length - 1].length != 2 && domArr[domArr.length - 1].search(knownDomsPat) == -1) {
                //alert("The address must end in a well-known domain or two letter " + "country.");
                return false;
            }

            // Make sure there's a host name preceding the domain.
            if (len < 2) {
                //alert("This address is missing a hostname!");
                return false;
            }
            // If we've gotten this far, everything's valid!
            return true;
        }