Unexpected lmtpproxy response

[Rob Mueller]

Every now and then, we see the following error in our logs:

Dec  6 22:29:20 www postfix/lmtp[15516]: 7319A58B2: to=<xyz>,
relay=/var/imap/socket/lmtpprox[/var/imap/socket/lmtpprox], delay=218,
status=bounced (host /var/imap/socket/lmtpprox[/var/imap/socket/lmtpprox]
said: 250 2.1.5 ok (in reply to DATA command))

We're currently using a hacked version of the lmtpproxyd.c to do proxied
delivery to our separate IMAP servers. The code is basically the same,
though we've replaced the mupdate lookup stuff with our own hostname
lookups.

There are a few specifics that seem to trigger it:
1. We're using a unix socket. If we change to an inet one with an internal
IP address, the problem doesn't seem to occur
2. The load of the destination lmtp server is quite high

We're running linux, so I'm not sure if it's a linux bug, some race
condition in the proxy or kernel, or anything else for that matter. Odd.
Just thought I'd check if anyone else has seen it or knows a work around.

Rob