Comment 1 for bug 715056

Thanks for reporting this.

This is caused by the mail-stack-delivery package's postinst script.

In theory, this should only happen when a main.cf backup file located at /var/backups/mail-stack-delivery/main.cf-backup could not be found, which would mean that i had not been installed before.

Unfortunately, this doesn't seem to be the case. This part of the postinst script is wrong:

 if [ -f "/etc/postfix/main.cf" ]; then
                if [ -e "$POSTFIX_BCKFILE" ]; then
                        mv $POSTFIX_BCKFILE ${POSTFIX_BCKFILE}-$(date +%Y%m%d%H%M)
                fi
         if [ -z "$2" -o ! -e "$POSTFIX_BCKFILE" ]; then

If the backup file exists, it renames it...but then checks to see if it exists again (which it doesn't, since it just got renamed)...