Postini is a cloud-computing email and Web security service currently owned by Google. It also offers email archival solutions.
Postini was formed as a small startup in 1999, but grew rapidly before being acquired by Google in 2007 for US$ 625 million. The company now delivers email messages weekly for millions of clients in companies across the globe.
Techopedia explains Postini
Client organizations that use Postini redirect their email receipt/delivery route to first go through Postini instead of their own email servers. Postini's advanced email scanners then scan the emails for viruses and other malware, filter out spam, identify and curb phishing attempts and stop directory harvest attacks before finally delivering the emails to the client's own email servers.
Postini uses sophisticated proprietary email scanning and pattern-gathering tools to analyze and classify email messages. However, even the service can sometimes erroneously classify email as spam, phishing attempts, and so on, and quarantine the email. In such cases, the client receives an automated alert, and can login to his or her account with Postini and release the message, as well as mark similar emails as "safe".