[Dovecot] mbox sync failure

[Alnis Morics]

Hi,

Yesterday I had to reboot my server machine and I think there was an email 
client connected from the LAN during the reboot which I did not notice then. 
Now that mailbox is no longer accessible: as soon as I try to connect, it 
lets me wait forever while openin the folder, and cycles endlessly this 
message in the logs:

Jul  2 19:40:37 myhostname dovecot: imap-login: Login: user=<username>, 
method=PLAIN, rip=#.#.#.#, lip=#.#.#.#, TLS
Jul  2 19:40:37 myhostname dovecot: IMAP(username): 
unlink(/var/mail/username.lock) failed: Permission denied
Jul  2 19:40:48 myhostname dovecot: IMAP(username): file mbox-sync.c: line 
1372 (mbox_sync_handle_eof_updates): assertion failed: (trailer_size
 <= 2)
Jul  2 19:40:48 myhostname dovecot: IMAP(username): Raw backtrace: imap 
[0x80b2081] -> imap [0x80b1f99] -> imap [0x807a536] -> imap [0x807ae71]
 -> imap(mbox_sync+0x422) [0x807d3c2] -> imap(mbox_storage_sync_init+0x3e) 
[0x807d8de] -> imap(imap_sync_nonselected+0x1c) [0x806446c] ->
imap(_cmd_select_full+0xc3) [0x805be83] -> imap(cmd_select+0x19) 
[0x805c059] -> imap [0x805d5ef] -> imap [0x805d690] -> imap(_client_input
+0x74) [0x805dd64] -> imap(io_loop_handler_run+0xf0) [0x80b7e20] -> 
imap(io_loop_run+0x18) [0x80b7338] -> imap(main+0x478) [0x8066388] ->
/lib/i686/cmov/libc.so.6(__libc_start_main+0xe5) [0xb7e36455] -> imap 
[0x8058561]
Jul  2 19:40:48 myhostname dovecot: child 2459 (imap) killed with signal 6

(I have Debian Lenny with dovecot 1.0.15.)

I tried to add the user dovecot to the group mail and give the group mail 
write permission to the mailbox. The permission errors stopped appearing but 
everything else is still there, including .lock file and 3 imap-login 
processes that resume as soon as I try to kill them.

There are also 2 unimportant mailboxes that still work.
I can view the beginning of the "username" mailbox with mc inner viewer, but 
it hangs as I go to the end of file.
Tried to copy the file so I could freely experiment with it but the copying 
hung up when it reached 87 % (the file is 1.1 GB). The copied part was 
unreadable.

Tried to

formail -ds < /var/mail/username >> /backup/usernameJul3

but with the same result.

Is there a way to repair the synchronization of the mbox? Or at least a way to 
recover its content?