There are three ways you can deploy an anti spam filter solution: On site spam filters - Spam filters are normally installed on your mail server, or on a separate machine inside your office. This adds to your internal administration costs, by adding another system you must maintain, patch, and backup. The IT Administrator has control over the entire system, but also has to take responsibility for it. Users call IT staff when they have a problem with spam and request that it be handled. Client side filters - Spam filters can also be installed on individual machines for filtering each users email. This gives the individual user the best control, but adds greatly to the cost (a license per machine), and requires even more maintenance for IT staff. It can also add to tech support costs internally as users mis-configure their own spam filter and request IT time to fix it. This solution is generally acceptable for home users, but not recommended for companies of more than a few people. Managed spam filter service (sometimes called a third party spam filter or MX spam filter ) - The spam filter is offsite and managed by a third party. The service should be robust, and have adequate resources to support your needs. Ideally the spam filter service should protect your systems from spammers, and provide backup capability in the event your server is offline. Administrators should also have full control over the settings for the entire domain. Ideally tagged spam should not require an Administrator to retrieve the email for a user. This can quickly become a resource drain as users want to check the quarantine to see if they missed any email. | 
