Domain content filtering allows you to create the same types of content filters as you can in My Content Filtering, but the filters added will be applied to all members of a domain. The evaluation of domain content filters happens before the evaluation of account-specific content filters. For more information about how to add a content filter, please refer to the Doteasy SmartMail Flash Tutorial: Setting Content Filters.
Note: Be aware that many users will prefer to set their own content filtering. You may want to minimize filtering at the domain level to filter only items that affect the entire domain.