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Advanced Direct Remailer (ADR) is a powerful remailer and mass mailer which send your message straight out to the recipient's mail server (without your ISP's SMTP server). ADR realizes multi-threaded direct delivery, and so works several times quicker than usual email client.

http://www.mailutilities.com/adr/ 

MailScan 5 for SMTP is the world's most advanced AntiVirus and AntiSpam Solution for Mail Servers that work on platforms like Windows, Unix, Linux, Novell and Solaris. It's installed on a Windows machine to act as a Security Gateway between your Mail Server and the Internet. MailScan 5 offers powerful features like Web Based Administration, Non Intrusive Learning Patterns and LDAP Authenticated Web Administration.