We have recently started using Trend Micro’s ERS service.
Basically email is passed to a Trend server, filtered against blacklists then passed onto your mail server.
You can setup other MX record to allow the mail to be forwarded to another mail server in times of outage.
Any email that the Trend server is unsure of is kept in a quarantine for I think around 7 days, allowing you to verify any legitimate email and adding spam to blacklists.
Your management console allows for reporting, and statistics to be generated allowing you to view everything from overall spam captured to single users spam amounts.
After viewing reports for the first month I have noticed a dramatic drop in our clients spam levels.
I am interested to know if anyone else is using this service and if so what there thoughts are on this service.
If you arn’t and are interested take a look at the following .pdf’s
http://us.trendmicro.com/imperia/md/content/us/pdf/products/enterprise/emailreputationservices/ers_3.6_gsg_post_2007-11-13.pdf
http://us.trendmicro.com/imperia/md/content/us/pdf/products/enterprise/networkreputationservices/ersh_1_gsg_post_2007-05-31.pdf
