Tumbleweed Communications on Tuesday followed in the footsteps of security rivals such as Symantec to launch an appliance that sits at the network edge and reduces up to 50 percent of the unwanted mail traffic before it hits enterprise mail servers.

MailGate Edge monitors such characteristics as the sender IP address, the number of connections, message volume, intended recipients, and other attributes across SMTP connections to identify bad behavior patterns. The appliance, said Tumbleweed, can reduce unwanted e-mail by 20 to 50 percent.

Directory Harvest Attacks (DHAs), for instance, often come from a relatively small number of IP addresses, and send a high number of messages with invalid recipients. (DHAs are brute force attempts by spammers to collect valid e-mail addresses from an organization or company, and involve sending thousands of messages with suspected addresses.) Such patterns can be spotted, and the traffic stopped.

MailGate Edge can block much of the Internet's "dark traffic," the term some give to the aggregate of spam, DHAs, mail denial-of-service attacks, and invalid SMTP packets. Tumbleweed claims that some 70 percent of all e-mail traffic is "dark."

Tumbleweeds 1U appliance analyzes SMTP traffic, a different approach than Symantec's recently-announced Mail Security 8160 appliance, which filters at the TCP/IP level, stopping spam on the spammer's servers rather than letting it reach the enterprise network.