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Old 7 Sep 2017, 03:23 PM   #4
Intergalactic Postmaster
Join Date: May 2004
Location: Irving, Texas
Posts: 8,440
Arrow How the spam filter really works

Leaving messages in the Spam folder does not affect spam filtering! I think you misunderstand how the Fastmail spam filtering system and personal Bayes database work. Refer to this section of the Fastmail help:

Until you get >200 spam and >200 non-spam messages reported, your personal Bayes database does not operate. Messages are reported to the Bayes database as follows:
  • Messages which are permanently deleted from the Spam folder are marked as spam in the database when they are permanently deleted. You can do this by manually permanently deleting messages in the Spam folder or using the auto-purge property for that folder.
  • Messages which are missed by the spam filter but marked by the user with the Report Spam button are automatically moved to the Spam folder and immediately marked as spam in the database.
  • Messages which are accidentally moved by the spam filter to the Spam folder but are then marked as Not Spam by the user are automatically moved to the Inbox folder and immediately marked as non-spam in the database.
  • Messages in folders whose property is set for spam learning are treated as follows. One time per day (I think it's usually in the night) all of your folders are scanned. If the folder is set for spam learning, any message which was added to that folder since the last daily scan is learned as specified in the folder properties. The message is only learned one time (the first time it is scanned after the message is added to that folder).
  • Fastmail strongly suggests that the Spam folder not be set up for automatic learning to prevent spam learning loops (read the Help for more details).
So if you have a pile of message in your Spam folder which were moved there by the automatic spam filter (or a user rule), those messages will not affect the spam filter until they are permanently deleted (unless you ignore the Fastmail directions to not set the Spam folder to be learned). The user flow which is best is:
  • Look at your Spam folder when it's convenient. Mark any non-spam as Not Spam and Delete Permanently any spam. Notice that when you in the Spam folder, the Delete button is changed to Delete Permanently.
  • If you rarely look at the spam folder you might miss good messages improperly filed into the spam folder. So it's good to check the Spam folder before any auto-purge folder setting permanently deletes the message. But remember that if you set the auto-purge to 365 days, the messages automatically filed into the Spam folder will not affect your personal Bayes spam filter until they have been there for one year. I don't thing that's what you intended!
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