How to spamproof a mailto link?

I want visitors to be able to click on (or copy) an email address directly on my webpage. However, if I could make it (a little bit) harder for bots and other crawlers to get said email address and register it in a spam list, it would be awesome.

I found different ways of doing this (i.e. encoding mailto HTML links), either with JavaScript or in pure HTML, but what do you guys recommend ? The JavaScript techniques seem more complicated, but this may potentially affect users that have it turned off, and legit crawlers like Google.

On the other hand, the HTML one seems a bit basic, the bot writers should have figured it out by now...

Should I bother at all doing this, or will the spammers get my email anyway ? I know that antispam filters are getting better and better, but if I can do something more to slow spammers down, I will.

JavaScript remains one of the best mailto obfuscator. For users with JavaScript disabled you may want to substitute the mailto link with a link to a contact form.

The following is a popular JavaScript anti spam email obfuscator:

• http://www.jottings.com/obfuscator/

There is also a php version of the above to be able to generate obfuscated emails from the server side.

This is the JavaScript code that the above tool would generate to obfuscate my email address (comments intact):

<script type="text/javascript" language="javascript">
<!--
// Email obfuscator script 2.1 by Tim Williams, University of Arizona
// Random encryption key feature by Andrew Moulden, Site Engineering Ltd
// This code is freeware provided these four comment lines remain intact
// A wizard to generate this code is at http://www.jottings.com/obfuscator/
{ coded = "[email protected]"
  key = "1DtzZ8TGBuhRjJMKWI4gkUF2qidfOyPmSN7X30Vpso6xvErLnwQCbalA95HcYe"
  shift=coded.length
  link=""
  for (i=0; i<coded.length; i++) {
    if (key.indexOf(coded.charAt(i))==-1) {
      ltr = coded.charAt(i)
      link += (ltr)
    }
    else {     
      ltr = (key.indexOf(coded.charAt(i))-shift+key.length) % key.length
      link += (key.charAt(ltr))
    }
  }
  document.write("<a href='mailto:"+link+"'>Email Me</a>")
}
//-->
</script><noscript><a href='contact-form.html'>Email Me</a></noscript>

This looks like a really cool method that encodes the characters, which I assume would defeat basic spam bots:

http://robspangler.com/blog/encrypt-mailto-links-to-stop-email-spam/

So

<a href="mailto:[email protected]">Email</a>

becomes

<a href="&#x6d;&#97;&#105;&#108;&#x74;&#111;&#58;&#116;&#101;&#115;&#116;&#x40;&#x74;&#101;&#115;&#x74;&#x2e;&#x63;&#111;&#109;">Email</a>

It's appealing in that it doesn't require any Javascript.

Plunker example here.

Building on Daniel Vassallo's answer, one way to encrypt a mailto link that may avoid cleverer spambots that will evaluate JS document.writes (as pointed out by incarnate) would be to put the decryption in a Javascript function that is only evaluated when the link is clicked on. For example, using base64 as the "encryption":

<script>

  function decryptEmail(encoded) {
  
    var address = atob(encoded);
    window.location.href = "mailto:" + address;
  
  }
  
</script>

<a href="javascript:decryptEmail('dGVzdEB0ZXN0LmNvbQ==');">Email</a>

Working Plunker.

I don't claim to know whether this could or could not be outsmarted by a more sophisticated crawler.

You could use the reCAPTCHA Mailhide functionality. This will render email addresses on the form [email protected] where the ellipsis is a link to view the full address. It is a little cumbersome for the visitor but should give premium protection. Having said that, this technique will not let your visitors copy the address directly from your webpage.

I don't get the part about the "legit crawlers" like Google. At least, I am unable to see why Google should index the email address anyway. (See OPs comment below.)

You can use external services like aemail.com:

> @email is a free e-mail hiding service that hides emails using short > URLs redirecting senders to the mailto-url after clicking the link.

After entering an email at aemail.com, you will get a short URL, which can be used to replace your 'mailto' link. Once link is clicked, your user will be redirected to the 'mailto' URL without any notice of the aemail.com. API can be used to hide emails/get URLs dynamically.

Example:

<a href="mailto:[email protected]">Contact</a>

Replaced With

<a href="https://aemail.com/q2">Contact</a>

Will Keep Email Link Working.

I simply use:

<script language="javascript" type="text/javascript">
var pre = "hideme";
document.write("<a href='mailto:" + pre + "@domain.com'>" + pre
+ "@domain.com</a>");
</script>
<noscript>Enable javascript to see our email!</noscript>

My version generates the link on the fly from a base64-encoded email string when the user hovers over the link, or if on a mobile device, touches it. All links with the attribute 'data-gen-email' will work.

// The string is your base64-encoded email
const emailAddress = atob("bWFpbHRvOnlvdUBkb21haW4uY29t");

// Select all links with the attribute 'data-gen-email'
const emailLinks = document.querySelectorAll('[data-gen-email]');

emailLinks.forEach(link => {
	link.onmouseover = link.ontouchstart = () => link.setAttribute('href', emailAddress);
});

You can encode your email to base64 by using btoa('mailto:[email protected]'), or elsewhere on the web:

btoa('mailto:[email protected]'); // "bWFpbHRvOnlvdUBkb21haW4uY29t"

Example link in html:

<a href="#" target="_blank" data-gen-email>Email Me!</a>

//This sets the mailto link when clicked. 
//As the link is followed, the focus is also lost and the link reset to # 
//html should look like this :
//<a class="courriel" data-courriel="john" data-objet="Just a test" href="#">Some text</a>

$('.courriel').click(function() { 
  var sA = $(this).attr('data-courriel'); // get nickname
  var sO = $(this).attr('data-objet');    // get subject
//Adresses are hard coded here; a nick name is used; 
//this to prevent having a potentially decypherable encoded adress  in the <a> tag
  switch (sA) { 
    case 'john': 
      $(this).attr('href', 'mailto:[email protected]?subject=' + sO);
	  break;
	case 'paul':
      $(this).attr('href', 'mailto:[email protected]?subject=' + sO);
      break;
    default:
		$(this).attr('href', '#');
  }
			
		
})
$('.courriel').focusout(function() { //reset the link to # on focus loss
	$(this).attr('href', '#');
})