dovecot - Sep 2010 - unwanted maildir directory

Dovecot-2.0.3 reported:

Error: Maildir: Found unwanted directory /path/to/mail/user/cur/:2,FST, but
rmdir() failed: Directory not empty

and sure enough, this directory really does exist and contain a valid message
file:

# cd /path/to/mail/user/cur/
# ls -lR
total 384
drwx------   8 vmail  vmail    272 Sep 24 09:06 .
drwx------  13 vmail  vmail    442 Sep 24 09:06 ..
-rw-------   5 vmail  vmail  41045 Sep 24 08:44
1285336100.M879758P1166.my.mail.server,S=41045,W=41755:2,RST
-rw-------   5 vmail  vmail  41045 Sep 24 08:44
1285336100.M910424P1166.my.mail.server,S=41045,W=41755:2,RST
-rw-------   5 vmail  vmail  41045 Sep 24 08:44
1285336337.M656599P1166.my.mail.server,S=41045,W=41755:2,ST
-rw-------   5 vmail  vmail  41045 Sep 24 08:44
1285336355.M88818P1164.my.mail.server,S=41045,W=41755:2,FS
-rw-------   1 vmail  vmail  14953 Sep 24 09:00
1285336838.M483116P5720.my.mail.server,S=14953,W=15225:2,
drwx------   3 vmail  vmail    102 Sep 24 09:00 :2,FST

./:2,FST:
total 88
drwx------  3 vmail  vmail    102 Sep 24 09:00 .
drwx------  8 vmail  vmail    272 Sep 24 09:06 ..
-rw-------  5 vmail  vmail  41045 Sep 24 08:44
1285335855.M242128P1165.my.mail.server,S=41045,W=41755
#

Dovecot must have created this non-Maildir++-ish directory, but why, why in cur/
not tmp/, and why didn't it clean it up?  (Not the "Directory not
empty" error specifically; I mean in the larger sense.)

Hm, I found more revealing errors after sending that message.  These are
scrubbed a little differently, to show two user names:

imap(pid 5720 user user1): Error:
open(/path/to/mail/user2/tmp/1285336854.M157825P5720.my.mail.server) failed: No
such file or directory
imap(pid 5720 user user1): Error: Maildir: Symlink destination doesn't
exist:
/path/to/mail/user2/cur/1285336100.M879758P1166.my.mail.server,S=41045,W=41755:2,FS
imap(pid 5720 user user1): Error:
open(/path/to/mail/user2/tmp/1285335855.M242128P1165.my.mail.server,S=41045,W=41755)
failed: No such file or directory
imap(pid 5720 user user1): Error: Maildir: Symlink destination doesn't
exist:
/path/to/mail/user2/cur/1285336337.M656599P1166.my.mail.server,S=41045,W=41755:2,FST
imap(pid 5720 user user1): Error:
open(/path/to/mail/user2/tmp/1285335855.M242128P1165.my.mail.server,S=41045,W=41755)
failed: No such file or directory
imap(pid 5720 user user1): Error: Maildir: Symlink destination doesn't
exist:
/path/to/mail/user2/cur/1285336337.M656599P1166.my.mail.server,S=41045,W=41755:2,FST
imap(pid 5720 user user1): Error:
open(/path/to/mail/user2/tmp/1285335855.M242128P1165.my.mail.server,S=41045,W=41755)
failed: No such file or directory
imap(pid 5721 user user2): Error: Maildir: Found unwanted directory
/path/to/mail/user2/cur/:2,FST, but rmdir() failed: Directory not empty
imap(pid 5721 user user2): Disconnected: Internal error occurred. Refer to
server log for more information. [2010-09-24 09:07:23] bytes=1268/173293

Note that user1 != user2.  Seems like this might be caused by having:
service imap {
  client_limit = 5
  service_count = 0
}

On Fri, 2010-09-24 at 09:59 -0500, Mike Abbott wrote:
> ./:2,FST:
> total 88
> drwx------  3 vmail  vmail    102 Sep 24 09:00 .
> drwx------  8 vmail  vmail    272 Sep 24 09:06 ..
> -rw-------  5 vmail  vmail  41045 Sep 24 08:44
1285335855.M242128P1165.my.mail.server,S=41045,W=41755
> #
> 
> Dovecot must have created this non-Maildir++-ish directory, but why,
> why in cur/ not tmp/, and why didn't it clean it up?  (Not the
> "Directory not empty" error specifically; I mean in the larger
sense.)
I've heard some people having similar directories in cur/ directory..
It's always been with people who have migrated from Courier, so I've
thought that the problem was that they just had accidentally
misconfigured something in the past and just didn't notice those extra
dirs with Courier.

So are you saying that this directory was actually created by Dovecot?
The directory name is ":2,FST" i.e. the base filename is empty. I
guess
this could happen if readdir() returns a "" directory entry while
reading new/ and then Dovecot does:

rename(".../new/", ".../cur/:2,")

that's about the only explanation I can think of for this.. I'll add a
check against this anyway just to be sure. :)

> Oh, interesting.. What about if you run it with two users?
With two users that same assertion trips.  One user runs fine.