If the general effectiveness of spam detection declines, it is most likely related to the following issues:
Ensure that PureMessage is using the latest anti-spam engine package by navigating to the page in ffthe PureMessage Manager, clicking Query to see if an update is available for the PureMessage-AntiSpam-Engine. If there is, run pmx-setup at the command line to install the available update(s).
Ensure that PureMessage is using the latest anti-spam data package by navigating to the page in the PureMessage Manager, and examining the date of the PureMessage-AntiSpam-Data package. It should be the current day's date. If it isn't, check the page, as described above, and update the package.
The issues described above affect overall spam detection. To troubleshoot a specific message, see "Why didn't PureMessage quarantine a message that is spam?" Also, see "Deployment Strategies" in the Getting Started Guide for information about configuring message-specific aspects of spam detection, such as whitelists, blacklists and custom anti-spam rules.