LinuxQuestions.org - Postfix emails send outgoing mail with wrong domain name

I just configured my first postfix mail server today. Everything is working correctly except for the fact that on all outgoing emails instead of the mail format being user@mydomain.biz it says user@hostnameofpostfixserver. I've looked everywhere I can think and I cant see where I'm substituting the host-name of the server for the domain name of my email. Where else could it be?

Below is my main.cf. I am running ubuntu 9.10.

# 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

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

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

myorigin = mydomain.biz [ substituted mydomain for actual domain ]
inet_interfaces = all
myhostname = mail.mydomain.biz [ substituted mydomain for the actual domain ]
mydomain = mydoamin.local [ substituted mydomain for the actual domain ]
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = mydomain.biz, localhost.localdomain, , localhost, 1upLinux [ substituted mydomain for the actual domain ]
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +

relayhost =
inet_protocols = ipv4