Antispam company Postini said it is now rejecting more than half of all attempts to send e-mail to its customers, due in part to increased activity from compromised home computers that have been turned into "zombies" for sending unsolicited commercial or "spam" e-mail.
The company is dropping 53% of all e-mail connections that use the SMTP (Simple Mail Transfer Protocol) without reading the content of the e-mail messages. That's an almost 20% increase since the company began aggregating information about troublesome internet addresses from across its customer base, said Andrew Lochart, director of product marketing at Postini.
The company manages e-mail for around 3,300 companies and 5 million e-mail users. Postini uses its own algorithms to spot spam, as well as denial of service attacks and other threats, by analysing the behavior of internet-connected machines attempting to send e-mail and, after that, the message content.
Since October, 2003, the has been aggregating information on Internet Protocol (IP) addresses of machines attempting to e-mail its customers, and dropping connection attempts from IP addresses that are behaving suspiciously without ever receiving the intended message. Since that time, the percentage of dropped connections swelled from around 35% of all connections to the current 53% , he said.
"We're cross-correlating spam and virus attacks for all our customers, and that allows us to block an even greater percentage of messages without even looking at the content," he said.
Home computers connected to the internet through large internet service providers are responsible for around 36% cent of all the dropped connections. Loosely configured machines called "open relays", and other compromised computers account for the rest of the dropped connections, he said.
Of the 47% of e-mail connections that are accepted, around 76% of the mail accepted are spam and 1%-2% are viruses. Only 11% of the 10.75 billion SMTP connections the company receives each month are for legitimate e-mail messages, Postini said.
Paul Roberts writes for IDG News Service