For our small software company's email, we use Google's Postini service that runs $12/mail account/year. Emails are routed to Postini which filters the spam an

For our small software company's email, we use Google's Postini service that runs $12/mail account/year. Emails are routed to Postini which filters the spam and then passes the good messages on to our mail server. It was pretty straight forward to setup by updating DNS and configuring the Postini account. I don't recall having do do anything special on the mail server or mail clients, but it has been a while.