Open Radar

 
The user says:

"
The best clue that I have to what might have caused the problem is that I recently deleted a bunch of old folders - including some with names like 'Junk' and 'Junk Mail', that had accumulated through various transitions between service providers over the years. I can't see exactly how that would have caused this copying behavior but it's the most relevant event I can think of.
"

Summary:
This issue made the tech news over the weekend - original blog post here:

http://blog.fastmail.fm/2013/10/26/mac-os-10-9-infinity-times-your-spam/

In short - the client is copying messages from the Junk folder into the Junk folder, and then expunging the old copies.  It has done it so often that when I first investigated there had been over 100,000 copies of a single message created and then expunged.  Our server keeps all messages for a week, causing over 2Gb of metadata to be stored for that folder.

The user has now been contacted and replied with more detail of their setup:

"Hi,

Interesting.  I had noticed the junk mail folder fill up and had purged it a couple of times, but clearly this is beyond that.

I have just checked my mail.app for plugins (~/Library/Mail/Bundles) and there are none.

Also, I have no rules relating to spam or the spam folder.  The only mail clients I use are mail.app on the Mac and Apple's iOS ones.

I'm happy to help diagnose the problem.  Is there anything else I can check for you?

Thanks."

Steps to Reproduce:
This only occurs on the one account.  The user is willing to help you debug what's wrong with their mail metadata.

Of course, corruptions happen - so it's more a matter of appropriate mitigation in the code rather than fixing the problem this one user has.

Expected Results:
We well-behaved internet application checks to make sure that it is not creating an infinite loop.  In this case, I would expect the client to notice that it's trying to move messages to the same folder that they are currently in, and abort.  In C I would write something like:

if (!strcmp(dest_foldername, src_foldername))
  return ERROR_ID;

Actual Results:
The mail client is causing an infinite loop of actions to the server, using legal IMAP commands.

Version:
ID ("name" "Mac OS X Mail" "version" "7.0 (1816)" "os" "Mac OS X" "os-version" "10.9 (13A603)" "vendor" "Apple Inc.")

Notes:


Configuration:
Server is Cyrus IMAPd, FastMail custom edition (currently version 9:1fmwheezy30246-9438-6fe50bc6)