Postfix suddenly stopped working

[Petr Janda]

Thanks, but my problem is different. It doesnt get anywhere near the 
local daemon, its like postfix listens on port 25, but when you try to 
connect to it, it will not respond.

One of the emails i sent to it just timed out over night with this error:

Connected to 220.233.111.100 but connection died.

Jon Hamilton wrote:
Petr Janda <elekktretterr at xxxxxxxxxxxxxx>, said on Fri Jul 28, 2006 [05:00:51 AM]:
} I use Postfix on my mailserver, and all of sudden(no change in configs, 
} no software updates done) it stopped working.
} 
} Thunderbird says that it is Connected to the server for about 2 minutes 
} and then connection failed. Output of tcpdump shows this:

I had what may be a similar issue; I found that postfix's "local" daemon
would stick.  In my case, "local" is configured to deliver through procmail, 
but it would occasionally just get stuck (it wouldn't get as far as calling
procmail in this case).  Sometimes a postfix stop and restart would work,
sometimes not.  Sometimes, a postmaster -h <first entry in queue> followed
by postmaster -H <same entry> would unclog things (that is postfix-speak for
"put it on hold" and "take it off hold" (moves it to a different queue
directory and back).  Sometimes a reboot was required.

I never did get to the bottom of it.  I rebuilt postfix and all of its
dependencies, with no change in behavior.  I did not ktrace the process,
but gdb told me that it was sticking on an flock - I never did figure out
which file though. 

This was all after upgrading from 1.2.x to 1.4 (and then 1.6).  In the end,
I ran out of time to monkey with it and just switched to sendmail.  I've still
got the postfix installation in place and intend at some point to get
back to troubleshooting it, just because it's weird.  If anyone has
suggestions for specific things to look at, I'd be happy to piddle with it 
and post output/results.  I can't trigger it on demand but in the course of
a day's worth of incoming email, it seems to happen 3-4 times, so it
shouldn't take too long to get some data.