On Tue, Jan 15, 2013 at 11:35:14PM +0800, Fred Ho wrote:
> Hi Wietse,
> I have already asked the ISP, they said it's not the problem on
> their side. It's mailgate2 our receiving side that is slow.The
> postfix 2.5.6 running in mailgate2 does not turn on any header_check,
> body_check checking. Plainly delivery to the backend.
In other words they told you to go away and stop bothering them.
The real issue is that neither MTA is "slow". What is slow is almost
certainly the transmission of the message payload across the network.
You need to use tcpdump to capture inbound port 25 traffic:
root# IP=192.0.2.1 # Replace with your MTA's IP
root# tcpdump -s0 -w pkts.pcap \
tcp and \
"(" "(" dst port 25 and dst host $IP ")" or \
"(" src port 25 and src host $IP ")" ")"
let this run for 10 minutes, then hit "CTL-C" and look at the
capture file. Note any retransmissions, and how quickly data is
arriving over the network, and whether your TCP is every closing
the TCP window, or whether bandwidth is low even though your TCP
window is wide open. Be aware that window scaling may be in place,
and is perhaps mishandled by a broken firewall (or when you read
the TCP capture without seeing the initial handshake, in addition
to the long sessions already in progress look at the window-scaling
negotiated by new sessions).
--
Viktor.
