Ecco main.cf:

program_directory = /usr/sbin
command_directory = /usr/sbin
daemon_directory = /usr/lib/postfix
mail_owner = postfix
default_privs = nobody
mail_spool_directory = /var/spool/mail
mailbox_command = /usr/bin/procmail
myhostname = mail.dominio.it
mydomain = dominio.it
myorigin = $mydomain
mydestination = $myhostname, localhost.$mydomain, $mydomain
inet_interfaces = all
smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU). Ciao Davide!!
default_transport = smtp
mynetworks = 127.0.0.1/8, 192.168.0.0/24
relayhost = [mail.infinito.it]
notify_classes = resource, software, bounce, policy, protocol
defer_transports = smtp
local_destination_concurrency_limit = 2
default_destionation_concurrency_limit = 10
masquerade_domains = $mydomain
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
#sender_canonical_maps = hash:/etc/sender_canonical
#virtual_maps = hash:/etc/virtual

Ecco un po di info:

-->File di zona:
$TTL 604800
dominio.it. IN SOA dominio.it. admin.dominio.it (
1 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ) ; Negative Cache TTL
NS dominio.it.
MX 10 mail.dominio.it.

ns IN A 192.168.1.2
mail IN A 192.168.1.2
www IN A 192.168.1.2

-->portatile:~# ping mail.dominio.it
PING mail.dominio.it (192.168.1.2) 56(84) bytes of data.
64 bytes from ns.dominio.it (192.168.1.2): icmp_seq=1 ttl=64 time=0.033 ms
64 bytes from ns.dominio.it (192.168.1.2): icmp_seq=2 ttl=64 time=0.058 ms
64 bytes from ns.dominio.it (192.168.1.2): icmp_seq=3 ttl=64 time=0.058 ms

--- mail.dominio.it ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 0.033/0.049/0.058/0.014 ms

-->portatile:~# telnet mail.dominio.it 25
Trying 192.168.1.2...
telnet: Unable to connect to remote host: Connection refused

-->portatile:~# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
220 mail.dominio.it ESMTP Postfix (Debian/GNU).
quit
221 Bye
Connection closed by foreign host.

-->portatile:~# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination

Chain FORWARD (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination