
<!-- START HIDE
<!-- Version 1.1:  Sandeep V. Tamhankar (stamhankar@hotmail.com) -->
<!-- This script and many more are available free online at -->
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function f_EmailCheck (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 represents the range of characters allowed as
       the first character in a valid username or domain.  I just made it
       the same as above, but if you want to add a different constraint,
       you would change it here. */
    var firstChars=validChars
    /* 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=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
    /* The following string represents at atom (basically a series of
       non-special characters.) */
    var atom="(" + firstChars + validChars + "*" + ")"
    /* The following string represents one word in the typical username.
       For example, in john.doe@somewhere.com, john and doe are words.
       Basically, a word is either an atom or quoted string. */
    var word="(" + atom + "|" + quotedUser + ")"
    // The following pattern describes the structure of the user
    var userPat=new RegExp("^" + word + "(\\." + word + ")*$")
    /* 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 course 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("The email address '" + emailStr + "' you entered is invalid")
    	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.")
        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
    var domainArray=domain.match(domainPat)
    if (domainArray==null) {
    	alert("The domain name doesn't seem to be valid.")
        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).
       If there's a country code at the end of the address, the full domain
       must include a hostname and category (e.g. host.co.uk or host.pub.nl).
       If it ends in a .com or something, make sure there's a hostname.*/
    
    /* 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.")
       return false
    }
    
    /* If it ends in a country code, we want to make sure there are at
       least 2 atoms preceding it (representing host and category (i.e.
       com, gov, etc.)) 
    if (domArr[domArr.length-1].length==2 && len<3) {
       var errStr="This address ends in two characters, which is a country"
       errStr+=" code.  Country codes must be preceded by "
       errStr+="a hostname and category (like com, co, pub, pu, etc.)"
       alert(errStr)
       return false
    }*/
    
    /* If it just ends in .com, .gov, etc., make sure there's a host name.
       This case can never actually happen because earlier checks take
       care of this implicitly, but we'll do it anyway. */
    if (domArr[domArr.length-1].length==3 && len<2) {
       var errStr="This address is missing a hostname!"
       alert(errStr)
       return false
    }
    // If we've gotten this far, everything's valid!
    return true;
}
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