[Dovecot] Mbox corruption - Inbox beginning with 'FFrom' or 'FrFrom'

[Erik Kratzenberg]

> On Tue, 2010-07-20 at 08:42 -0400, Erik Kratzenberg wrote:
>> I experienced this today with my own IMAP folder, so maybe being able to
>> offer a more specific order of events will help.  Also not sure if I
>> previously mentioned that this is occasionally happening with IMAP
>> folders even though it's much more common under POP3.
>>
>> 1) I had just cleaned out my Junk folder.
>> 2) Two messages were received without error.
>
> So basically what POP3 clients usually do, delete everything. Does the
> mailbox have the "FOLDER INTERNAL DATA" message at the beginning?

It did not and still doesn't, after having more messages received.

>> 3) I marked the folder as read in Thunderbird.
>> 4) I restarted Thunderbird
>> 5) The next delivery attempt to that mailbox (using dovecot deliver)
>>      failed:
>>
>>      save failed to Junk: Mailbox isn't a valid mbox file
>>
>> The odd thing is that the delivery *did* succeed because that message is
>> in there.
>
> Or maybe you just got two of those same messages? :) I don't think it
> could have written it after giving this error.

Well, it had the exact same Message ID and also had several deliveries 
afterwards that succeeded before I tried to access the mailbox again 
with IMAP.

>>    The very first message header is the one that was corrupted
>> which always seems to be the case.  Does "deliver" read/write the entire
>> mbox file or just append the new message to the end?
>
> deliver first checks that the mbox file is valid by reading and
> verifying the From_-line at the beginning of the file. If it's ok, then
> it appends to end of file. The corruption most likely happened during
> the expunge, not in deliver.
>
> Hmm. See what it logs with attached patch?

I'll get that patch added and let you know.  Thanks.