function isEmpty(inputStr) {
	if (inputStr == "" || inputStr == null) {
		return true	
	}
	return false
}
 function select(field) {
 	field.focus()
 	field.select()
 }

<!-- Changes:  Sandeep V. Tamhankar (stamhankar@hotmail.com) -->

/* 1.1.2: Fixed a bug where trailing . in e-mail address was passing
            (the bug is actually in the weak regexp engine of the browser; I
            simplified the regexps to make it work).
   1.1.1: Removed restriction that countries must be preceded by a domain,
            so abc@host.uk is now legal.  However, there's still the 
            restriction that an address must end in a two or three letter
            word.
     1.1: Rewrote most of the function to conform more closely to RFC 822.
     1.0: Original  */

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

<!-- Begin
function emailCheck (field) {
	var emailStr = field.value
	if (!isEmpty(emailStr)) {
		/* 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) {
		  /* 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)")
			select(field)
			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 username doesn't seem to be valid.")
			select(field)
		    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!")
				select(field)
				return false
			    }
		    }
		    return true
		}

		// Domain is symbolic name
		var domainArray=domain.match(domainPat)
		if (domainArray==null) {
			alert("The domain name doesn't seem to be valid.")
			select(field)
		    return false
		}

		/* domain name seems valid, but now make sure that it ends in a
		   three-letter word (like com, edu, gov) or a two-letter word,
		   representing country (uk, nl), and that there's a hostname preceding 
		   the domain or country. */

		/* Now we need to break up the domain to get a count of how many atoms
		   it consists of. */
		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>3) {
		   // the address must end in a two letter or three letter word.
		   alert("The address must end in a three-letter domain, or two letter country.")
			select(field)
		   return false
		}

		// Make sure there's a host name preceding the domain.
		if (len<2) {
		   var errStr="This address is missing a hostname!"
		   alert(errStr)
		   select(field)
		   return false
		}

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