How does SpamSieve interact with iCloud

SpamSieve
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1

I am confused about using SpamSieve with AppleMail and iCloud. Does SpamSieve download unfiltered email to my Mac, apply filters, and then upload the filtered email to iCloud? And then the filtered emails become available on my iPad and iPhone via iCloud. Or is some other mechanism in use?

2
  1. Apple Mail on all your devices downloads unfiltered mail from iCloud. (They are all syncing with the IMAP server.)
  2. SpamSieve reads the new messages in Mail on the Mac and analyzes them.
  3. SpamSieve tells Mail to move the spam messages to the Junk mailbox.
  4. Mail moves them locally and on the IMAP server. (Nothing is uploaded; it just tells the server to move the messages.)
  5. The other devices notice that the messages have been moved and move them, too.