We had na old notebook runing Ubuntu 12.04 working as a web/ftp/mail server and it worked but since the notebook was a notebook and pretty old and unreliable, a desktop was bought to replace it before it stopped working all together.

Due to issues with the new desktop's vídeo card, we couldn't use Ubuntu 12.04 so we installed Ubuntu 13.10 and wen't about configuring it.

Since we removed the notebook from the network, we kept the same Computer Name and local IP address to make things as close to the old server as possible configuration-wise.

However, something has gone wrong since Postfix is throwing error 451 4.3.0 lookup faillure on every attempt to send a mail, and no email can be received either.

Our main.cf file is a copy of the one we were using (and working) on the old server (notice we use EHCP)

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name powered by Easy Hosting Control Panel (ehcp) on Ubuntu, www.ehcp.net
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no
myhostname = m21-traducoes.com.pt
relayhost = 
mydestination = localhost, 89.152.248.139
mynetworks = 127.0.0.0/8, 192.168.0.0/16, 172.16.0.0/16, 10.0.0.0/8,  89.152.248.0/24
virtual_alias_domains = 
virtual_alias_maps = proxy:mysql:/etc/postfix/mysql-virtual_forwardings.cf, proxy:mysql:/etc/postfix/mysql-virtual_email2email.cf
transport_maps = proxy:mysql:/etc/postfix/mysql-virtual_transports.cf
virtual_mailbox_domains = proxy:mysql:/etc/postfix/mysql-virtual_domains.cf
virtual_mailbox_maps = proxy:mysql:/etc/postfix/mysql-virtual_mailboxes.cf
virtual_mailbox_base = /home/vmail
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions = permit_mynetworks,permit_sasl_authenticated,check_client_access hash:/var/lib/pop-before-smtp/hosts,reject_unauth_destination
smtp_use_tls = yes
smtpd_use_tls = yes
smtpd_tls_auth_only = no
smtpd_tls_CAfile = /etc/postfix/cacert.pem
smtpd_tls_cert_file = /etc/postfix/smtpd.cert
smtpd_tls_key_file = /etc/postfix/smtpd.key
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom
virtual_create_maildirsize = yes
virtual_mailbox_extended = yes
virtual_mailbox_limit_maps = proxy:mysql:/etc/postfix/mysql-virtual_mailbox_limit_maps.cf
virtual_mailbox_limit_override = yes
virtual_maildir_limit_message = "The user you are trying to reach is over quota."
virtual_overquota_bounce = yes
debug_peer_list = 
sender_canonical_maps = 
debug_peer_level = 1
proxy_read_maps = $local_recipient_maps $mydestination $virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps $virtual_mailbox_domains $relay_recipient_maps $canonical_maps $sender_canonical_maps $recipient_canonical_maps $relocated_maps $mynetworks $virtual_mailbox_limit_maps $transport_maps

alias_maps = hash:/etc/aliases

smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated,check_client_access hash:/var/lib/pop-before-smtp/hosts,reject_unauth_destination
smtpd_destination_concurrency_limit = 2
smtpd_destination_rate_delay = 1s
smtpd_extra_recipient_limit = 10
disable_vrfy_command = yes
smtpd_delay_reject = yes
smtpd_helo_required = yes
smtpd_error_sleep_time = 1s
smtpd_soft_error_limit = 10
smtpd_hard_error_limit = 20

This configuration was working before but now everytime i try to send a mail in squirrelmail it reports:

Message not sent. Server replied: 
Requested action aborted: error in processing
451 4.3.0 <[email protected]>: Temporary lookup failure

And i can't send mail to it from outsider either. Any ideas?

EDIT: Here are some issues MXToolBox reports to my domain, answering hopefully to @Teun Vink:

              BlackList      Mail Server     Web Server    DNS
  Error           4              0               2          0
  Warnings        0              0               0          3
  Passed          0              6               3          12

So the domain is on some blacklist, but that doesn't explain the error at all No mail server issues found (except it's not working) Those two web server errors it's because i don't have HTTPS workin (No SSL Certificate) so the test fails Those 3 DNS warnings we're already there when it was working with the other machine and are related to stuff i can't control:

   SOA Refresh Value is outside of the recommended range
   SOA Expire Value out of recommended range
   SOA NXDOMAIN Value too high

I've searched and as far as i can tell only the guys who sold the retail can change those values and they won't.

Edit2: I half solved the issue.on the new machine postfix was installed but postfix-mysql waasn't so he couldn't connect to the database (rookie mistake). After fixing that, i can now send mails to the outsider without any issues, however i am still not able to receive mails from utside. The sender doesn't get any message warning about the non-delivery but the message doesn't fall in the inbox and the log shows:

Nov 13 15:11:57 m21-traducoes postfix/smtpd[5872]: NOQUEUE: reject: RCPT from re
lay4.ptmail.sapo.pt[212.55.154.24]: 451 4.3.5 <relay4.ptmail.sapo.pt[212.55.154.
24]>: Client host rejected: Server configuration error; from=<[email protected]>
 to=<[email protected]> proto=SMTP helo=<sapo.pt>
Nov 13 15:11:57 m21-traducoes postfix/smtpd[5872]: disconnect from relay4.ptmail
.sapo.pt[212.55.154.24]