The Junk folder may require an additional step. If you don’t have junk mail filtering enabled, then Mail will ignore your requests to use any folder as the Junk folder (an error notice explaining what’s going on would be useful here, fellas). But if you’ve already got your mail host (e.g. Gmail) filtering your spam for you, you may not want to use Mail’s less-accurate built-in filtering.

Here’s the trick to make it work: enable Junk Mail filtering, and make sure the option set is “Move it to the Junk mailbox”. Then in the main window, choose which folder you want to use for Junk mail as described above. It will move up top.

Then, return to account preferences, and under Junk Mail, change the option to Perform Custom Actions. Then click Advanced… and change the rule from “Message is Junk Mail” to something that will never be true, e.g. “Message Type is RSS Article” (if you don’t use Mail for RSS feeds), or “Date Sent is greater than 1000 days old”. Now you can have Mail recognize your mail host’s spam folder without actually doing its