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Re: Is everyone else seeing duplicates?

Hi Mark,

On Wed,  5/Dec/01 20:29:25, mdevin@ozemail.com.au wrote:
> On Tue, Dec 04, 2001 at 11:57:57AM -0800, Empty One wrote:
> > I realise this may be a little late, it being the
> > fourth and all, but i'm a behing in reading the list. 
> > Are you sure you aren't leaving the origional message
> > on the server?  I know that with some mail programs,
> > every time you scan the server for new messages, it
> > keeps adding the message, and leaving it in the
> > server, creating the problem you are describing.
> >
> No, my fetchmail is configured to not keep the messages on the server -
> so that is not it.
> Actually, it seems to be better now.  I think what was actually doing it
> was that my firewall was checking for "unclean" packets with this rule:
> iptables -A INPUT -i $EXT_IF -m unclean -j log_unclean
> But apparently this is broken in the 2.4.14 kernel, which I just
> happened to upgrade to.  What happened as a result was that my firewall
> kept blocking a whole heap of "unclean" packets.  I think that this may
> have been stuffing up fetchmail by making it resend the messages.
> But I could be wrong.  The thing is that it seems to have gotten better
> after I got rid of this rule in the firewall.  And I haven't changed my
> /etc/postfix/main.cf, fetchmailrc, or .procmailrc files from what they
> were when it was still happening.
> Hmmm?????
> Cheers.
> Mark.

Is your mail server protected by netfilter firewall? If so, I'm suppose that
problem of duplicating mail is caused by netfilter. Let's consider following

1) Remote mail server connects to local mail server and sends a mail.
2) Local mail server store the mail.
3) Mail servers exchange FIN packets.
4) Because of netfilter error (closing connections too early) one of FIN
packet is dropped.
5) Remote server repeats transfer as it supposes that connections wasn't
completted so mail is duplicated.

I observe small amount of duplicated mail and dropped FIN packets which seems
belonging to legal connections. However I haven't checked if there is
correlation between dropped packets and duplicated mail.

Someone would like to comment?


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