qmail bounce and dr web query

[bigblue]

Hi,

I'm fairly new to Plesk, but hopefully someone can help me out as I've never really needed to get my hands 'dirty' before!

I'm running Plesk 8.2.1 on a VPS, hosting 2 domains. The first domain has been running with no problems for the past year, and I've just recently added a second domain which is also running fine.

Since the 14th July, I've been receiving on average 3 mail daemon failure notices per day (I've already received 3 separate mails today alone!). Below is a copy of the mail that I receive (ip and host address blanked out for obvious reasons).

Can someone advise a complete Plesk newbie what is causing this to happen all of a sudden and to help me out to fix it? There appears to be 2 things going on - 1. qmail send program is bouncing all over the place and 2. Unable to chdir to maildir. (#4.2.1) - whatever that is!

Any help/advise really appreciated!

Thx

Here's the mail:
=================
Hi. This is the qmail-send program at lvps212-241-***-***.vps.myhost.co.uk.
I tried to deliver a bounce message to this address, but the bounce bounced!

<anonymous@lvps212-241-***-***.vps.myhost.co.uk>:
Sorry, no mailbox here by that name. (#5.1.1)

--- Below this line is the original bounce.

Return-Path: <>
Received: (qmail 7940 invoked for bounce); 16 Jul 2008 18:49:21 +0100
Date: 16 Jul 2008 18:49:21 +0100
From: MAILER-DAEMON@lvps212-241-***-***.vps.myhost.co.uk
To: anonymous@lvps212-241-***-***.vps.myhost.co.uk
Subject: failure notice

Hi. This is the qmail-send program at lvps212-241-***-***.vps.myhost.co.uk.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<drweb@lvps212-241-***-***.vps.myhost.co.uk>:
Unable to chdir to maildir. (#4.2.1)

--- Below this line is a copy of the message.

Return-Path: <anonymous@lvps212-241-***-***.vps.myhost.co.uk>
Received: (qmail 7933 invoked by uid 111); 16 Jul 2008 18:49:21 +0100
Date: 16 Jul 2008 18:49:21 +0100
Message-ID: <20080716174921.7930.qmail@lvps212-241-***-***.vps.myhost.co.uk>
From: root@lvps212-241-***-***.vps.myhost.co.uk (Cron Daemon)
To: drweb@lvps212-241-***-***.vps.myhost.co.uk
Subject: Cron <drweb@212-241-***-***> /opt/drweb/update.pl
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <HOME=/var/drweb>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=drweb>

Dr.Web (R) update details:
Update server: http://update.us.drweb.com/unix/433/433
Update has began at Wed Jul 16 18:49:01 2008
Update has finished at Wed Jul 16 18:49:21 2008

Following files had been updated:
/var/drweb/bases/dwntoday.vdb
/var/drweb/updates/drwtoday.txt
/var/drweb/updates/dwntoday.txt
/var/drweb/bases/drwtoday.vdb