Outbound mail issue

Question

I've set up mail and it works fine as long as we use it only intern. Frome one OD account to another.
However I'm not succesful in setting up a SMTP relay with our ISP's SMTP server. I get the following message in the SMTP log file of my server:
"Mar 31 20:02:24 server postfix/smtp[1250]: 5CF157C986: to=<[email protected]>, relay=uit.telenet.be[195.130.133.66]:25, delay=3331, delays=3331/0.12/0.12/0.04, dsn=4.1.8, status=deferred (host uit.telenet.be[195.130.133.66] said: 450 4.1.8 <[email protected]>: Sender address rejected: Domain not found (in reply to RCPT TO command))"
Can anybody help solving this issue.
Maybe following info helps:
erver:postfix h32$ postconf -n
command_directory = /usr/sbin
config_directory = /etc/postfix
content_filter =
daemon_directory = /usr/libexec/postfix
debugpeerlevel = 2
enableserveroptions = yes
html_directory = no
inet_interfaces = all
localrecipientmaps =
luser_relay = mone
mail_owner = _postfix
mailboxsizelimit = 0
mailbox_transport = cyrus
mailq_path = /usr/bin/mailq
manpage_directory = /usr/share/man
messagesizelimit = 10485760
mydestination = $myhostname,localhost.$mydomain,localhost,server.h32.str,h32.str
mydomain = h32.str
mydomain_fallback = localhost
myhostname = server.h32.str
newaliases_path = /usr/bin/newaliases
queue_directory = /private/var/spool/postfix
readme_directory = /usr/share/doc/postfix
relayhost = uit.telenet.be
sample_directory = /usr/share/doc/postfix/examples
sendmail_path = /usr/sbin/sendmail
setgid_group = _postdrop
smtpsasl_authenable = no
smtpsasl_passwordmaps =
smtpdenforcetls = no
smtpdpw_server_securityoptions = gssapi
smtpdrecipientrestrictions = permitsasl_authenticated,permit_mynetworks,reject_unauthdestination,permit
smtpdsasl_authenable = yes
smtpdtls_certfile = /etc/certificates/Default.crt
smtpdtls_keyfile = /etc/certificates/Default.key
smtpdtlsloglevel = 0
smtpduse_pwserver = yes
smtpdusetls = no
unknownlocal_recipient_rejectcode = 550

Answer 1

What needs to be done, depends on your ISP. Chances are that by authenticating against their server they will let you through. It is also possible they can whitelist you, but only your ISP can tell you.
That said, it is still not a good idea to use fantasy domain names for sending mails. Many receiving mail servers will block you even though you relay through your ISP.
"Internal use only" is open for interpretation. In your log snippet you show a mail destined to sogeti.be. This is not internal mail. Even if your ISP allows you to relay, it may be that sogeti.be's mx will block you. So unless all mail servers you need to send to are known and they are willing to whitelist you, it would be a good idea get a proper domain.
Alex