Okay, I'm confused.
As I remember this failed when I tested it the first time, but it now works for me:
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# Works for me...
tell application "Mail"
make new mailbox with properties {name:"Bar/Dandy/Jim"} -- Failed according to John Mitchell
end tell
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I tested this sometime before that, and it worked. (After Brian's post about the response from Apple support.)
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tell application "Mail"
make new mailbox at beginning with properties {name:"Testing Mailboxes/2015/01/02/03/04/Last Test Mailbox"}
end tell
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This also works.
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# Works for me.
tell application "Mail"
make new mailbox with properties {name:"Testing Mailboxes/2015/01/02/03/04/Last Test Mailbox"}
make new mailbox with properties {name:"Testing Mailboxes/2016/01/02/03/04/Last Test Mailbox"}
end tell
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