[Dovecot] Unexplained MDA bounce backs

[Dean Manners]

I have recently noticed that some of our internal mailer scripts are causing
Dovecot-LDA to generate Mailer Delivery Subsystem messages.  The following
Dovecot-LDA message is generated:


---- Message body ----
Your message was automatically rejected by Dovecot Mail Delivery Agent.
The following reason was given:
Unknown error
---- Message body ----

---- Message header ----
Return-Path: <MAILER-DAEMON>
Delivered-To: bounces at xxxxx
Received: by mymachine.xxxxx (Postfix, from userid 5000)
	id 5772568300; Mon, 14 Jan 2008 18:00:56 +1100 (EST)
Message-ID: <dovecot-1200294055-774265-0 at mymachine>
Date: Mon, 14 Jan 2008 18:00:55 +1100
From: Mail Delivery Subsystem <noreply at xxxxx>
To: <bounces at xxxxx>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=disposition-notification;
	boundary="21506/mailfilter02"
Subject: Automatically rejected mail
Auto-Submitted: auto-replied (rejected)
Precedence: bulk
---- Message header ----


Initially I thought these were being caused by Delivery-Receipt requests,
however have since tested this and is not the case.  I have tried to snoop
through the logs (unfortunately on a very busy mail hub) using the
Message-ID, however this doesn't seem to lead me back to the original
message - only the MDA notification.  I can only ascertain that its isolated
to our scripts, as the bounces@ address is specifically used by them.

Any ideas what would cause/trigger the "Unknown error" automatic rejects ?

System config is
-Postfix 2.3.4 with MySQL backend
-Dovecot 1.0.rc26 with MySQL backend, using only deliver.

All mail deliveries are otherwise fine.

Regards
__________________________________________ 
Dean Manners