[Dovecot] Re: New mail sometimes fails to appear

[Timo Sirainen]

On Tue, 2006-02-07 at 10:13 +0200, Tom Alsberg wrote:
> 4. Furthermore:  If the last message seen from within Thunderbird was
>    not yet read, and the problem occurs (new mail arrives that is not
>    seen), this last message will then seem corrupted from Thunderbird
>    - it will contain at the end some garbage filling, and then part of
>    the next message in the mailbox.
> 
>    This is while the mailbox itself is completely valid, has no such
>    garbage in it, and the messages are validly separated by an empty
>    line and a valid "From " line.  Perhaps this means there's some
>    race-condition bug in the mbox reading/index syncing code?  That's
>    the code I least understand as of now...
> 
>    Attached is an example of one such last message saved from
>    Thunderbird after new mail arrived that was not seen.  The filler
>    characters are bytes of 0x80, and then the next message from
>    "n-Path: " is present.

They're actually 0x00 inside the mbox file, but Dovecot just translates
them to 0x80 since IMAP doesn't allow sending 0x00 characters.

Now, these 0x00 characters are added to mbox file when it's rewriting
the headers and it figures out that it needs more space. So it first
grows the file by writing 0x00 characters to the end of the file. Then
it starts moving message data towards the end of file.

So you mean that this corruption is only seen by Thunderbird, and it
won't stay in the mbox file itself? In that case it means that mbox
locking isn't working properly, ie. a Dovecot process is reading the
mbox while another Dovecot process is modifying it. I don't remember
having tested mbox_read_locks=dotlock, but I'd have thought it would
have worked..