You can enable the debug mode of postfix smtp daemon ( http://www.postfix.org/DEBUG_README.html). Then you can see the request and response which postfix talked with your tcp_table script.
PS: From the postfix source code, it seems postfix has not received any response from your tcp_table. However postfix will retry 10 times for such scenario (sleep 1 sec before each retry). 2013/7/28 Wietse Venema <wie...@porcupine.org> > Zhang Huangbin: > > On Sunday, July 28, 2013 at 8:24 PM, Wietse Venema wrote: > > > > > 1) Use a network sniffer to see what Python actually sends. You may > > > assume that your program sends \n, but Postfix does not receive \n. > > > > Thanks Wietse, and John. > > I think this is the root cause, will try a network sniffer later. > > > 2) Unrelated to this bug: closing the connection after one request > > > is inefficient. > > > > My program closes the connection immediately. > > Caution: it is not a good idea to close a connection immediately > after writing data to it. Some TCP/IP implementations may discard > unsent data when a connection is closed. > > In Postfix, I avoid "write-close" bugs by keeping a connection open > until the receiver closes it (with of course a time limit that > forces the connection to be closed when things take too long). > > Wietse >
