Thanks John.
I asked remote MTA to do a tcpdump. They found that SBG would aborted the smtp session while transferring in process if the sesstion time exceeds 30s(our SBG session timeout is 30s). We tried to change session timeout to 120s, then aborted session at the timing of 120s while transferring in process.
In user guide 8.0, it says something about session time:
This setting controls how long the MTA waits for a request or response from the connecting MTA. If this limit is exceeded, the appliance will drop the connection.
My understanding was that the session timeout is about idle time(it says 'waitting'). However, it seems about sesseion time instead of idle time. Am I correct?
Thanks,
-Laowu