i have postfix set up as a satellite to listen on port 587 i can send email outside fine trough the postfix(ubuntu) box from the local network with no problems

when i try to connect to the postfix(ubuntu) box from a external ip and send mail it spits back a 554 5.7.1 Relay access denied error

i can telnet to it fine, just cant send mail

this is my main.cf :

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
append_dot_mydomain = no
readme_directory = no

smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options =
smtp_use_tls = no

myhostname = cotiso-desktop
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = mydomainname.com, cotiso-desktop, localhost.localdomain, localhost
relayhost = smtp.mydomainname.com
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all 
inet_protocols = all

there is no security set up yet, i'm just trying to get it working first

any ideas?

thanks in advance