Try enabling the debug_logger and see what information it gives.
Thank your for your suggestion, it is useful.
I found this in maillog.
Apr 6 00:58:16 hg02 postfix/scache[7737]: statistics: start interval
Apr 6 00:54:46
Apr 6 00:58:16 hg02 postfix/scache[7737]: statistics: domain lookup
hits=0 miss=2 success=0%
Apr 6 00:58:16 hg02 postfix/scache[7737]: statistics: address lookup
hits=0 miss=3 success=0%
Apr 6 00:58:16 hg02 postfix/scache[7737]: statistics: max simultaneous
domains=1 addresses=2 connection=2
Apr 6 00:58:21 hg02 postfix/postfix-script[9941]: refreshing the
Postfix mail system
Apr 6 00:58:21 hg02 postfix/postfix-script[9941]: refreshing the
Postfix mail system
Apr 6 00:58:21 hg02 postfix/master[14541]: reload -- version 2.6.5,
configuration /etc/postfix
Apr 6 00:58:21 hg02 postfix/anvil[7587]: statistics: max connection
rate 1/60s for (smtp:xxx.xxx.xxx.xxx) at Apr 6 00:57:44
Apr 6 00:58:21 hg02 postfix/anvil[7587]: statistics: max connection
count 1 for (smtp:xxx.xxx.xxx.xxx) at Apr 6 00:57:44
Apr 6 00:58:21 hg02 postfix/anvil[7587]: statistics: max cache size 3
at Apr 6 00:57:49
The postfix reload itself. Maybe this is the problem.
But i wonder why it reload auto.
yk