[Dovecot] Re: corrupt attachments

Brian Thompson brian at eng.wayne.edu
Wed Dec 7 13:36:49 EET 2005

Thanks Curtis, I didn't think about what would happen if
Sendmail tries to attach a new message to the bottom of the
mbox at the exact same time that Dovecot goes to rewrite an
attachment to the middle of the mbox. We are using fcntl()
over NFS for both Sendmail and Dovecot. The mail server
is the only NFS client that accesses the mail spools on the
fileserver, so there's no chance of another NFS client
causing issues. The only real reason we're using NFS is
because the fileserver gets backed up on a regular basis
but the mail server doesn't. The backups happen at night
and this phenomena was happening in the middle of the day,
so it's not a conflict with the backup software.

At first I thought the last four characters of every line were
getting cut off, but it turns out that the characters I thought
were missing were pushed to the next line. It appears that
Dovecot is shifting the position of the CRLF by four characters
- not necessary a problem or related to the corruption issue.

I have a "before" and "after" document in base64 format that
I wish I could post to the list, but the content of the decoded
document is somewhat confidential (it's a vendor quote).

The total number of characters in the good document is
7,006 and the total number of characters in the corrupt
document is 6,308. If it's a locking issue, I'd imagine that
as Dovecot is writing the attachment, it would get interrupted
and cut off, leaving only the first portion of the attachment
written and the corrupted (missing) portion would be the
tail end of the attachment.

In this case, comparing the two files visually character
by character, the missing characters are a solid chunk right
out of the middle. The beginning and end of the attachment
are correct. Sort of odd...


Curtis Maloney wrote:

> Just to check:
> it sounds like you're both using mbox format... have you verified that 
> Dovecot, your LDA, and anything else accessing the mailboxes is using 
> exactly the same locking, _in the same order_ ?
> -- 
> Curtis Maloney
> cmaloney at cardgate.net

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