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Actually, that's not quite true. Checking that box will prevent Mail from storing the messages it marks as Spam on the server, but will not affect that folder being synchronized to Mail from the server.

What email service are you using? It depends greatly on what configuration options you have available. If you're using Gmail, for instance, you can install the Labs feature for IMAP Folder Access that will let you tell it not to synchronize the Spam folder, or any other folder you don't want.

jW
 
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