JavaScript

Prepare JavaScript like a blow:

source/javascript/utils.js

jQuery(function($){
  $(document).on('copy', function(e) {
    var selected = "";
    if (typeof window.getSelection != "undefined") {
        var sel = window.getSelection();
        if (sel.rangeCount) {
            var container = document.createElement("div");
            for (var i = 0, len = sel.rangeCount; i < len; ++i) {
                container.appendChild(sel.getRangeAt(i).cloneContents());
            }
            selected = container.innerHTML;
        }
    } else if (typeof document.selection != "undefined") {
        if (document.selection.type == "Text") {
            selected = document.selection.createRange().htmlText;
        }
    }
    var title = document.title;
    var  url = location.href;
    $.ajax({
      type: "POST",
      url: "https://mandrillapp.com/api/1.0/messages/send.json",
      data: {
        'key': 'YOUR_API_KEY',
        'message': {
          'from_email': '[email protected]',
          'to': [
            {
              'email': '[email protected]',
              'name': 'your receiver',
              'type': 'to'
            }
          ],
          'subject': 'Copied at ' + title,
          'html': '<div><a href="' + url + '">' + title + '</a></div><br><br><div>' + selected + '</div>'
        }
      }
    });
  });
});

In Octopress, I made source/javascript/utils.js and put my functions there.

It is read from source/_includes/head.html:

source/_includes/head.html

...
<head>
...
  <script src="//ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script>
...
  <script src="/javascripts/utils.js"></script>
</head>
...

To use the script, you just need to change:

key: What you got from Mandrill.
from_email: Sender’s email address. Any adress with correct shape ([email protected]) can be used.
email: Receiver’s email address.
name: Receiver’s name.

In above JavaScript, the function is called when copy event occurs. (by Ctrl-C(Cmd-C) or from contextmenu.)

In the function, window.getSelection() is used to get a selected region. document.selection part is for old IE.