Postini - In-line infrastructure for pre-processing email messages in real time. Allows email management applications to be integrated into any SMTP email system. - http://www.postini.com/
MailTester.com - Online tool to test an e-mail address. Find out if is valid, why it bounces or what type of mailserver the mailbox is on. - http://mailtester.com/
Slugmail - An email based reminder service. - http://www.slugmail.com