Problems receiving emails from china...

Hi all,

I did a quick search of the archives and was unable to find any previous
discussions relevant to this topic.

One of our clients has been having problems receiving some legitmate
emails from business associates in China. The client's mailserver is
running qmail. In almost all of the cases, the failing email has at least
one attachment and is larger than what might be considered "normal". Our
client's mailserver receives part of the message and then the smtp
connection hangs and eventyally times out. Many times, the sending mail
server will attempt to send the message again and again before finally
giving up. The failing messages can be successfully delivered to hotmail
and/or yahoo accounts.

I've observed this problem while it was occuring and there are multiple
smtp connections open between the clients server and the sender's server.
The connections are in various states, some established, some in fin_wait,
etc. I've tried tracerouting to the sender's server and in every case I've
observed the trace times are terrible. I've looked at various aspects of
the mail server's configuration and all looks well there. I've even tried
having the senders email to a totally different mailserver on our network
and get similar failures. It's staring to look like this is just a simple
case of bad network connectivity from the sender. My guess is that the big
free email systems have relay servers all over the world, so the sender in
China would be talking to a server much closer to home. This would explain
why the mail can be successfully delivered to hotmail, yahoo, etc.

Has anyone ever experienced a problem similar to this? Thanks in advance
for your attention and any responses/help.


Have you tried checking the intervening path is clean w.r.t. ECN?



Is there similar problem existing with sending email
to email server inside china?

maybe you could check end-to-end delay and packet
loss rate.

Another method, ask your customer to cut the
attachment to several parts and send them seperately.


--- Lou Laczo <> wrote: