The San Carlos, Calif., company said that of the 23 billion messages it processed last month, 19.6 billion, or 84 percent, were unwanted. This amounted to a four-percent increase since February.
Postini reported that it thwarted more than 15 billion directory harvest attacks, or DHAs, a spamming technique in which an attacker guesses at possible email addresses within a domain. These attacks – up 7 percent from February – can cause a company's server to become bombarded with undeliverable mail, leading to a potential denial of service (DoS) event.
Exemplifying the rise in IM use among enterprises, Postini filtered more than 6.5 million IM conversations in March, up more than 200 percent from February.
"The increase of IM messages by 4.3 million in one month's time is a clear indication that more corporations are adopting IM as a business communications tool," said Andrew Lochart, senior director of marketing for Postini.
Meanwhile, the company said the number of viruses in email fell 19 percent in March, as Postini stopped 32.5 million bugs. The Mytob virus was halted 16.7 million times, followed by Netsky (5.3 million), Mimi (2.7 million), Lovgate (1.6 million) and Bagle (1.2 million).