I'm getting the mesage regulary inside mail.log from postfix. In special, but not only, at mails send received mailman.

warning: hostname localhost does not resolve to address ::1: No address associated with hostname

::1 as well as 127.0.0.1 are defined as localhost inside /etc/hosts -- as provided by openVZ.

Actually inside /etc/hosts these is configured (I removed special domains and IP for reasons):

fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

2a01::<some IPv6> host.example.org  host example.org

127.0.0.1 localhost.localdomain localhost
# Auto-generated hostname. Please do not remove this comment.
xxx.xxx.xxx.xxx host.example.org  host example.org
::1             localhost ip6-localhost ip6-loopback

And this seems to work:

$ host localhost
localhost has address 127.0.0.1
localhost has IPv6 address ::1

On this box bley is also running.