I added this to the file components/com_k2/controllers/item.php. In the places where I wrote something in caps, you need to put in the appropriate text for your site.

	function modemail() {
		global $mainframe;
  		$user   = &JFactory::getUser();
		$msgbody = 'To edit and publish items go to '.JURI::base().'REST OF PATH';	
		$sub  = 'A WEBSITE NAME item has been posted or edited';

    		$mail = &JFactory::getMailer();
	        $mail->addRecipient( 'EMAIL ADDRESS TO GET NOTIFICATIONS' );
	        $mail->setSender( array( $user->get('email'), $user->get('name') ) );
	        $mail->setSubject( $sub );
	        $mail->setBody( $msgbody );

		if ($mail->Send()) {
		  echo "Mail sent successfully.";
		} else {
 		 echo "An error occurred.  Mail was not sent.";
		}

		JRequest::checkToken() or jexit('Invalid Token');
		require_once(JPATH_COMPONENT_ADMINISTRATOR.DS.'models'.DS.'item.php');
		$model= new K2ModelItem;
		$model->save(true);
		$mainframe->close();
		
	}

And then in the file components/com_k2/views/item/tmpl/form.php, I added this between the Save button and the Cancel button in the toolbar table at the top of the page.

                  <?php if ($this->row->id):?>
                  <td id="toolbar-modemail" class="button">
                      <a class="toolbar" href="#" onclick="javascript: submitbutton('modemail'); return false;">
                      	<span class="icon-32-send" title="Notify Editors"></span>
                      	Notify Editors
                      </a>
                 </td>
                 <?php endif; ?>