when i look at qpsmtpd i can see where the email has hit the server and has gone through most of the "hand shaking". the last two lines of the given email is
second to last response 2010-10-21 13:51:11.978756500 12697 354 go ahead
last response - 2010-10-21 21:42:12 12697 Connection Timed out
This indicates the remote end didn't complete sending the body of the message to your server. I think the most likely cause of that is a badly configured firewall between your server and theirs, which blocks ICMP. Read this:
http://www.phildev.net/mss/mss-talk.pdfThe problem manifests as short messages getting through to your system, but longer ones causing a stall/freeze. So, for instance, the SMTP ehlo, 'mail from', 'rcpt to' completing, but the data stalling and timing out.
If you have a firewall between your SME server and the Internet, check its configuration, or get rid of it entirely.