You need to check certain logs, such as the application log in Event Viewer, on a daily basis. You can use the diagnostic logging function in Exchange System Manager to configure the detail of events that are logged. You need to check the message load on your Exchange Server 2003 servers and the logs generated by your virtual servers, and your antivirus product. You should also check the available disk space on volumes that store Exchange logs and databases.
You should monitor and review other logs and monitor information on a regular basis. You need to review performance logs and protocol logs, manage mailbox limits, manage the Badmail folder, and manage the postmaster mailbox. You can use HTTP Monitor to monitor Web sites and OWA servers.
On-demand maintenance is typically required when regular logging indicates a potential problem. Typically, you may need to defragment databases, check and restore database integrity, and deal with queuing issues.