The Quarantine happens at the system level.

Admin Login > Settings > Antispam > SMTP Blocking

But I don't quite understand collecting the HIGH probability of spam vs LOW priority of spam. You'll get more false positive insight on lower scored messages. 

the Quarantine for SMTP can currently only be activated for outgoing messages,

I was asking to be able to "quarantine" the messages that are classified as "High Spam" based on the scores, because they are usually always correct but gradually there are "false positives" and it would be useful to be able to check them and quickly unblock them from the system quarantine

Mark, so I understand your requesting a quarantine on incoming messages. There might be a way to do this via events. I'm not 100 percent positive though.

It is also useful to have multiple quarantine folders.   I use a downstream system to implement my quarantine because it provides a message review interface.   High risk and medium risk are separate categories.  Medium risk gets  more thorough admin review because it has more false positives, but errors can appear in either bucket.

Hey Guys, 

Thanks for the question. The quarantine is currently only for outbound messages. I will go ahead and submit a feature request to allow you to quarantine high spam messages. 

Kind Regards,