function emailCheck (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 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 adresinizi yanlış girdiniz. (@ ve . işaretlerini kontrol ediniz.)");
      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("Kullanıcı adı kısmında (@ işaretinden önce) hatalı bir karakter kullandınız.");
         return false;
      }
   }

   for (i=0; i<domain.length; i++)
   {
      if (domain.charCodeAt(i)>127)
      {
         alert("Alan adı kısmında (@ işaretinden sonra) hatalı bir karakter kullandınız.");
         return false;
      }
   }

   // See if "user" is valid 

   if (user.match(userPat)==null)
   {
      // user is not valid
      alert("Kullanıcı adı (@ işaretinden önceki kısım) hatalı.");
      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("Verilen IP adresi geçersiz!");
            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("Alan adı (@ işaretinden sonraki kısım) hatalı.");
         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("Adres geçerli bir alan adı uzantısı veya iki harften oluşan ülke koduyla bitmelidir..");
      return false;
   }

   // Make sure there's a host name preceding the domain.

   if (len<2)
   {
      alert("Adreste sunucu adı bulunamadı.");
      return false;
   }

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