me.com moving junk to a different folder

For some time now I find that some of my my (good and bad) messages are randomly moved to a folder called “junk” inside a “.Mac” folder in Apple Mail.
I have the Apple Junk filter disabled and am very happy with SpamSieve which moves Spam into a “Spam” folder inside a folder “On My Mac”
I can’t find a solution to this on the Apple support site and wonder if someone here has one.
Thanks

The MobileMe/.Mac server has its own spam filter that moves messages into the Junk mailbox. It used to be possible to turn this off, but when Apple updated the MobileMe Web interface (this past summer, I think) they removed that option. So, in short, the only way to prevent this from happening is not to use MobileMe, although there is a workaround to make it appear as though all the spam messages are in the same mailbox.

For another workaround, see the Apple Mail - Server Junk Mailbox script.