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.
Eyvind Bernhardsen