Weird slowness

Hey,
I just installed postfix, configured it and testing now.
If I telnet localhost or from the DMZ I happily See the following:
220 monet1.ngv.vic.gov.au ESMTP Postfix
quit
221 Bye
Connection closed by foreign host.

Which is fairly speedy and looks fine

If I telnet from outside of our DMZ I get:
220 ***********************************
quit
502 Error: command not implemented

There is a delay of about a second or so.

Any ideas?

Adam

# postconf -n
alias_database =3D hash:/etc/postfix/aliases
alias_maps =3D hash:/etc/postfix/aliases
command_directory =3D /usr/sbin
config_directory =3D /etc/postfix
daemon_directory =3D /usr/libexec/postfix
debug_peer_level =3D 2
inet_interfaces =3D 10.10.10.20, localhost
local_recipient_maps =3D proxy:unix:passwd.byname $alias_maps
mail_owner =3D postfix
mailq_path =3D /usr/bin/mailq.postfix
manpage_directory =3D /usr/share/man
mydestination =3D $mydomain, $myhostname, localhost.$mydomain
mydomain =3D ngv.vic.gov.au
myhostname =3D monet1.ngv.vic.gov.au
mynetworks =3D 127.0.0.1/8, 10.10.10.0/24, 172.16.7.0/24, 172.16.8.0/24,
172.16.22.0/24
myorigin =3D $myhostname
newaliases_path =3D /usr/bin/newaliases.postfix
proxy_interfaces =3D 203.18.1.25
queue_directory =3D /var/spool/postfix
readme_directory =3D /usr/share/doc/postfix-2.0.16/README_FILES
sample_directory =3D /usr/share/doc/postfix-2.0.16/samples
sendmail_path =3D /usr/sbin/sendmail.postfix
setgid_group =3D postdrop
transport_maps =3D hash:/etc/postfix/transport
unknown_local_recipient_reject_code =3D 450