When you use a tag-and-deliver strategy to battle spam, you'll want to give users an automated way to handle the spam they receive. Message-handling rules are one way to automate this task. Rules operate in two modes: client side and server side. As the classifications imply, the mail server (e.g., Exchange Server) processes and performs server-side rules; the client (e.g., Outlook) processes and performs client-side rules. A rule's mode is determined by the action assigned to the rule. For example, if you create a rule to move a message to a folder within the mailbox, then the rule is a server-side rule because the mail server can perform this action without Outlook running. If you create a rule to move a message to a folder within a .pst file, then the rule is a client-side rule because Outlook needs to be running to access the .pst file. When defining spam-handling rules, you should use the Move to folder operation and select a destination folder on the Exchange server for the following reasons:
- Rule actions such as Delete and Flag message are client-side actions. Choosing these actions leaves messages in the Inbox until Outlook can process the rule. If a person has a Research In Motion (RIM) BlackBerry device or other wireless email device, spam will reach the handheld device.
- If users want to delete messages identified as spam, they should use the Move to folder action and specify the Deleted Items folder as the target. This approach lets the system remove the message but keeps the rule on the server side. When spam is moved into the Deleted Items folder, the messages still count toward the mailbox storage limit, and the messages will remain in the Deleted Items folder until you run the Mailbox Manager or use Outlook to empty the folder.
For example, if you use an IMAP connection on a Windows-based mobile device, spam will be downloaded to that device. If server-side rules are defined, Exchange will move the messages out of the Inbox, preventing them from being forwarded or downloaded to the handheld device because the Inbox is usually the only folder that the redirection and synchronization processes reference.