Mail Storage Guard is an extension for Microsoft Exchange 2000/5.5 and IIS SMTP servers, designed to protect your mail server from spam, prevents mail relaying, mail bomb and NDR attacks. Support extended blacklists with wildcards; public DNS blacklists (ORDB, SPEWS, SPAMCOP and others); can reject all \"misaddressed\" mail (recipient not listed in Active Directory) at SMTP level or point its to postmaster; and many other features.