[Dovecot] LSUB "" "" vs LIST "" "" (hacked Apple Mail problem)

[Eyvind Bernhardsen]

The LSUB command does not act like LIST when provided with an empty  
mask argument.  LIST responds with the hierarchy delimiter:

	* LIST (\Noselect) "." ""
	OK List completed.

whereas LSUB doesn't return anything useful:

	OK Lsub completed.

RFC 3501 doesn't specify what LSUB should do in this case, but  
Courier IMAP has LSUB act like LIST.  The attached patch modifies  
imap/cmd-list.c to make Dovecot do the same.


Why do I care about LSUB?  I'm using a hack for Apple Mail that  
replaces its LIST command with LSUB (something like what's described  
here: http://www.macosxhints.com/article.php? 
story=20040407062603804), to prevent it from syncing public folders  
from the Exchange server at the office.

The hack replaces _all_ LISTs with LSUBs, including the LIST "" ""  
Mail.app sends to discover the hierarchy delimiter.  Since dovecot  
doesn't give it any information in response to LSUB "" "", Mail.app  
defaults to using "/" as a delimiter, which means that trying to  
access a subfolder only results in an "Invalid mailbox name" error.

While this isn't really a bug in Dovecot, it's not inconceivable that  
other people than me could be affected by this problem  
(macosxhints.com has a substantial readership).  It's also tricky to  
diagnose, especially since the "Invalid mailbox name" message doesn't  
include the invalid mailbox name, so any bug reports you get are  
likely to eventually be filed under "crazy [Mac] users".

In fact, while Googling to figure out why Dovecot wasn't working for  
me, I came across at least one poster to this mailing list who had  
discovered that Mail.app was using "/" as a delimiter.  I can't be  
sure, but I'm guessing that his problem was related to mine.

Since the patch is tiny and doesn't hurt performance or make Dovecot  
do anything that contradicts the IMAP RFC, I hope you'll consider  
adding it to the official distribution.

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Eyvind Bernhardsen