I then re-ran the iredmail install script and it went without a hitch.

Cheers, Des.

I have been trying to install iRedMail but keep getting the following error:

The following NEW packages will be installed:
  postfix-mysql
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
Need to get 43.4kB of archives.
After this operation, 77.8kB of additional disk space will be used.
Get:1 http://mirror.sov.uk.goscomb.net lenny/main postfix-mysql 2.5.5-1.1 [43.4kB]
Fetched 43.4kB in 0s (1091kB/s)
Selecting previously deselected package postfix-mysql.
(Reading database ... 29530 files and directories currently installed.)
Unpacking postfix-mysql (from .../postfix-mysql_2.5.5-1.1_i386.deb) ...
Setting up postfix-policyd (1.82-2) ...
dbconfig-common: writing config to /etc/dbconfig-common/postfix-policyd.conf
*** WARNING: ucf was run from a maintainer script that uses debconf, but
             the script did not pass --debconf-ok to ucf. The maintainer
             script should be fixed to not stop debconf before calling ucf,
             and pass it this parameter. For now, ucf will revert to using
             old-style, non-debconf prompting. Ugh!

             Please inform the package maintainer about this problem.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO).
unable to connect to mysql server.
error encountered creating user:
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
dbconfig-common: postfix-policyd configure: aborted.
dbconfig-common: flushing administrative password
dpkg: error processing postfix-policyd (--configure):
subprocess post-installation script returned error exit status 1
Setting up postfix-mysql (2.5.5-1.1) ...
Adding mysql map entry to /etc/postfix/dynamicmaps.cf
Errors were encountered while processing:
postfix-policyd
E: Sub-process /usr/bin/dpkg returned an error code (1)
< ERROR > Installation failed, please check the terminal output.

Following the Wiki tips, as I have an existing MySQL database, I have changed the following:

export MYSQL_FRESH_INSTALLATION='NO'   
export MYSQL_ROOT_PASSWD='MyPassword' 

Any ideas why policyd is failing?

Cheers, Des.