Postfix issue - local domains

[baboonish]

I'm wondering if I've configured something incorrectly. If a user of one domain on my server sends an email to a user on another domain who's DNS records are held by my server but mx records point elsewhere, the mail is sent to my postfix server on the same machine.

Is there a way of having postfix check the mx record and send accordingly before checking whether the domain is handled by this machine?

postconf -n as follows:

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
config_directory = /etc/postfix
inet_interfaces = all
inet_protocols = all
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
mydestination = /etc/mail/local-host-names
myhostname = web1.hostfife.net
mynetworks = 127.0.0.0/8
myorigin = /etc/mailname
recipient_delimiter = +
relayhost =
smtp_tls_note_starttls_offer = yes
smtp_tls_session_cache_database = btree:${queue_directory}/smtp_scache
smtp_use_tls = yes
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject _unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
smtpd_sasl_security_options = noanonymous
smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem
smtpd_tls_auth_only = no
smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.crt
smtpd_tls_key_file = /etc/postfix/ssl/smtpd.key
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_database = btree:${queue_directory}/smtpd_scache
smtpd_tls_session_cache_timeout = 3600s
smtpd_use_tls = yes
tls_random_source = dev:/dev/urandom

setup is postfix on ubuntu server 7.

Peter

[till]

If you created a site for this domain in ISPConfig, you will have to set the mailserver to external in the site settings (on the options tab) AND also set all co-domains of this site to external mailserver (on the options tabs of every co-domain).