Sybari's Advanced Spam Defense (ASD) works with your existing Microsoft Exchange servers. Installation is flexible and should suit a network of any size. For smaller companies, ASD can sit on the Exchange Server. Larger companies can install it as a remote pass-through server (the Gateway) with a Service Center controlling any Gateways on the network.
The Gateway's job is to sift incoming email and discard any that matches a spam signature. It talks directly to the Service Center to receive updates and policy.
Blocking email is mostly an automated affair, with ASD's anti-spam engine doing most of the work using updated information from Sybari's servers. This means that there is little management to spam blocking, but there are times when you'll want to get your hands dirty.
In these cases, management is performed through an IIS web server application, so you can use it from anywhere in your company without having to install a dedicated management application.
Should you want to, you can create your own policies to allow or deny email from specified locations. These rules have priority over the inbuilt defenses, so you need to be very careful when creating them.
One neat feature is the ability to quarantine messages that cannot be determined as spam in a user's "ASD junk mail" Outlook folder. They can then allow or deny the email manually. The results feed back into the spam engine.
From a pure spam point of view, ASD is a great application. It uses Sybari's expertise in detecting spam, rather than forcing you to come up with rules. The user tools are great, too, as they let human beings make decisions without increasing management workload.
But spam is all it deals with. It doesn't take into account the larger picture of content filtering, so you cannot scan outgoing emails for banned content, prevent attachments or integrate with anti-virus. Without all the tools to enforce corporate policy, you will still need another package to do the full job.