How Often Does SpamSieve Drone Refresh?

Hi:

Anyone have an idea how often Apple’s Mail program goes through the IMAP “TrainSpam” and “TrainGood” folders to clean them out, as described in section 5.5.7 Setting Up a Spam Filtering Drone of the excellent manual?

Thank you!

Mail will check each time it receives a new message in the inbox.

Thank you!
Appreciate it.