Serious Postfix weirdness

[Petr Janda]

Hi all,
I have got reports about lost mail(not received, im the receiver not the 
sender) recently and trying to find out whats going on seems to be beyond me.

Basically a lot of email is lost with "timeout after DATA"

For example:
timeout after DATA (0 bytes) from mail.securepay.com.au[203.89.212.166]

.  Supposedly the problem here is that the sending machine has got a firewall 
in front of it thats blocking ICMP MUST FRAGMENT. I somewhat could verify 
this by trying to ping those machines and indeed pinging them does not work. 
On the Postfix website it suggests lowering MTU, so I lowered it from 1500 to 
1000, but this did not improve the situation at all. Some suggest disabling 
PIPELINING, so i did that but it didnt work either.

I took a tcpdump of one of these and attached it to this email. (daria is the 
name of the mail server)

The system is running DragonFly 2.0.0 with ETHER_INPUT_CHAIN and ETHER_INPUT2 
enabled.

Just a note about my setup: The server is running behind a Cisco ADSL Router 
that connects to a Cisco switch and the server connects to the switch.

Any Postfix gurus here that could help me figure this problem out?

Thanks,
Petr
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