POPFile must have a minimum of two buckets which, most often, are named spam and allowed or spam and inbox. Note that “unclassified” is not counted as one of the two minimum buckets. “Unclassified” is only used by POPFile when it cannot make a solid determination as to which bucket an email should be assigned. There is, effectively, no maximum number of buckets.

See also:

• How long will it take until POPFile will reach a decent accuracy?
• Bucket Setup