The Validates Email Veracity Of plugin validates that e-mail addresses are correctly formatted. It also checks email domain MX records to prevent mistypes.
This plugin is covered in chapter 7 of Practical Rails Plugins; you can also find out more at the Validates Email Veracity of homepage.
Author: Carsten Nielsen
Installation:
ruby script/plugin install http://svn.savvica.com/public/plugins/validates_email_veracity_of