> It was when this failure occured, I changed the hostname to bl5400, and
> tried again same result.
I strongly suspect that somewhere in one or more of your system's configuration files, that old numeric host name still exists.
Please confirm that the old numeric hostname has been edited into the new hostname (that starts with a letter) from *all* configuration files on your machine under /etc, including /etc/hosts , /etc/mailname , /etc/aliases and /etc/postfix/main.cf
> It was when this failure occured, I changed the hostname to bl5400, and
> tried again same result.
I strongly suspect that somewhere in one or more of your system's configuration files, that old numeric host name still exists.
Please confirm that the old numeric hostname has been edited into the new hostname (that starts with a letter) from *all* configuration files on your machine under /etc, including /etc/hosts , /etc/mailname , /etc/aliases and /etc/postfix/ main.cf