// Source: http://www.gladir.com/CODER/JAVASCRIPT/isemail.htm
function IsEmail(Email) {  
    if((Email == null) || (Email.length == 0)) return false;
     for(I = 0; I < Email.length; I++) {   
        switch(Email.charAt(I)) {
                case " ":case "\t":case "\n":case "\r":
               case "(":case ")":case ":":case ",":case "/":case "'":case "\"":
               case "~":case "`":case "!":case "#":case "$":case "%":case "^":
               case "&":case "*":case "+":case "=":case "[":case "]":case "{":
               case "}":case "|":case "\\":case "?":case "<":case ">":
                     return false;
          }
    }
     
     for(ArobasFound = 0, I = 1; I < Email.length; I++) if(Email.charAt(I) == "@") {
          ArobasFound++;
          if(ArobasFound == 1) AfterArobas = I;
     }
    if(ArobasFound!=1) return false;
    AfterArobas += 2;
    while ((AfterArobas < Email.length) && (Email.charAt(AfterArobas) != ".")) AfterArobas++;
    if((AfterArobas >= Email.length - 1) || (Email.charAt(AfterArobas) != ".")) return false;
    else return true;
}

// Call emailCheck(this.email.value, false)

<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->

<!-- V1.1.3: Sandeep V. Tamhankar (stamhankar@hotmail.com) -->
<!-- Original:  Sandeep V. Tamhankar (stamhankar@hotmail.com) -->

<!-- Begin
function emailCheck (emailStr, bAffAlert) {
	/* 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 john.doe@somewhere.com, 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) {
		if (bAffAlert) {
			/* 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) {
			if (bAffAlert) {
				alert("Ths username contains invalid characters.");
			}
			return false;
	   }
	}
	for (i=0; i<domain.length; i++) {
		if (domain.charCodeAt(i)>127) {
			if (bAffAlert) {
				alert("Ths domain name contains invalid characters.");
			}
			return false;
	   }
	}

	// See if "user" is valid 
	if (user.match(userPat)==null) {
		if (bAffAlert) {	
			// 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) {
				if (bAffAlert) {
					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) {
			if (bAffAlert) {
				alert("The domain name does not seem to be valid.");
			}
			return false;
		}
	}

	if (checkTLD && domArr[domArr.length-1].length!=2 && 
	domArr[domArr.length-1].search(knownDomsPat)==-1) {
		if (bAffAlert) {
			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) {
		if (bAffAlert) {
			alert("This address is missing a hostname!");
		}
		return false;
	}

	// If we've gotten this far, everything's valid!
	return true;
}

//  End -->