Postfix -- Mail relay issue

I have been running this Ubuntu 6.06 (ISPconfig, Postfix) server for over 2 years now. I followed your "Perfect..." docs. I must say, the best around... Thank you.
About a month ago I started receiving sporadic emails that my server had been spamming.... My VSP notified me the other day and I have been going through my configs for the last 3 days now.

I have a Virtual Server out on the internet with my own public IP. I am hosting about 5 websites. Only 3 of them use mail. 2 of them are using my server as the the SMTP relay for their mail client.

I was wondering if someone could point me in the right direction?

here is my postfix main.cf

#
# 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 (Ubuntu)
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

# TLS parameters
smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.crt
smtpd_tls_key_file = /etc/postfix/ssl/smtpd.key
smtpd_use_tls = yes
smtpd_tls_session_cache_database = btree:${queue_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${queue_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.

myhostname = mail.mydomain.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
# mydestination = mail.mydomain.com, localhost.mydomain.com, localhost
relayhost =
mynetworks = 127.0.0.0/8
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
### Limit sent/recieved emails to 100 Megs "(header+body+attachment)x(mime-encoding) <= 100 meg"
message_size_limit = 102400000
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
smtpd_sasl_local_domain = $myhostname
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions =
permit_sasl_authenticated,
permit_mynetworks,
reject_unauth_destination
smtpd_tls_auth_only = no
smtp_use_tls = yes
smtp_tls_note_starttls_offer = yes
smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom

virtual_maps = hash:/etc/postfix/virtusertable

mydestination = /etc/postfix/local-host-names
​

Any help would be greatly appreciated.
Thank you
Tony