The Mail Server Update for Mac OS X Server 10.3.9 delivers overall improved reliability, and is recommended for all Mac OS X 10.3.9 servers.
You can update your server in one of two ways: Use Software Update or update from a standalone installer.
Software Update installation
Software Update may have referred you to this document. For more information on using this feature, see "Mac OS X: Updating your software."
Because some updates are prerequisites for others, you may need to use Software Update more than once to get all available updates.
Standalone Installer
A standalone installer is also available from Apple Downloads.
This update addresses an issue in which cyrus mail services on Mac OS X Server 10.3.9 may eventually stop working, leaving the mail database in an unsettled state after the cyrus mailbox database has been reconstructed.
If you have already encountered mail server issues, you should reconstruct the cyrus mailbox database using these steps: