It is a configuration option within Clam that is enabled by default with SmarterMail. It results in too many false positives. You need to add the following to the Clam conf file:

PhishingScanURLs no

Hopefully the false-positive problem can be reduced by the filter creators.  We *reluctantly* turned off the Phishing URL scans, but that will let a lot of garbage now slip through.  The quarantine had a LOT of legitimately bad phishing-related emails, and it's a shame they won't be stopped now-- at least not by Clam.

But there were too many important messages from legitimate senders (including American Express, Nationwide Insurance, Marriot, AppRiver, etc.) that after careful examination, we verified never should have been quarantined.  

The trapped messages from AppRiver were quarantine notices.  Quarantine notices being quarantined... oh, the irony.  For those not familiar with AppRiver (SpamLab) they are a 3rd party "premium" spam filtering service some of our customers subscribe to.