Getting an email notification when a new Drush version is available
If you go to the Drush project page on Drupal.org then you can follow the "Releases" RSS feed found at the bottom of the page.

EDIT

You can also use the IFTTT.com service if you want the e-mails.  Just set up a rule on the site so that when the RSS feed gets updated, it sends you an e-mail.