Hi Victor, Wietse, OK, I have reloaded postfix with the new settings.I will perform the tcpdump to capture the inbound messages and see.Thanks for all the suggestions.
Regards,Fred​ On Wed, 01/16/2013 12:00 AM, Wietse Venema <[email protected]> wrote: > Viktor Dukhovni: > > 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). > > Victor has an excellent point. > > You can quickly eliminate TCP window scaling issues by dumbing down > Postfix thusly: > > # postconf -e master_service_disable=inet > # postfix reload > # postconf -e tcp_windowsize=65535 master_service_disable= > # postfix reload > > You need to execute all four commands in the given order. > > (You can also eliminate TCP window scaling issues with kernel > configuration). > > Wietse > >
