There I go praising spam system Akismet, and then this story appears on the Computerworld site. It highlights one of the critical issues with nearly all spam systems - that you must train them properly, and go through the folder or quarantine mechanism that you use to filter out and identify the false positives.

Certainly, from the details we know in this story, it seems that the quarantine folder wasn't checked regularly enough to identify completely valid emails.

This is an extreme example of when things can go wrong, but simpler and less drastic issues can arise, like missing an important email, or an email lying in the quarantine folder for years before it is finally passed and released.