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Date:      Wed, 8 Dec 1999 16:03:51 +0200 (SAT)
From:      John Hay <jhay@mikom.csir.co.za>
To:        stevenf@shellnet.co.uk (Steven Fletcher)
Cc:        freebsd-net@FreeBSD.ORG
Subject:   Re: Very odd problem with email.
Message-ID:  <199912081403.QAA81133@zibbi.mikom.csir.co.za>
In-Reply-To: <277A0E0FE38ED311A66A00A0C9D43A3D0781F5@data.shellnet.co.uk> from Steven Fletcher at "Dec 8, 1999 11:36:43 am"

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> 
> I have now tried what I consider to be 'everything' - swapping the
> mailserver hardware, swapping the POP3 server that we use (tried QPOP &
> Cucipop - QPOP emails are getting slightly further than those delivered via
> Cucipop). Running tcpdump on both the affected machines (the mailserver &
> the external machine) shows that ACK's don't seem to be getting through:
> 
> 16:42:31.530365 194.129.209.11.pop3 > www5.shellnet.co.uk.4969: P
> 1590:2928(1338) ack 35 win 17520 (DF)
> 
> Is repeated at increasing intervals after the file stops.

One possibility is that the path mtu discovery is getting screwed up
somewhere. That may happen if some link have a smaller mtu that your
local net and icmp NEEDFRAG packets are blocked.

John
-- 
John Hay -- John.Hay@mikom.csir.co.za


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