Postfix can't send mails from outside to my server - relay access denied

I can't send mail from an external mail to my postfix mails..

Oct 16 15:44:17 mail postfix/smtpd[18600]: connect from externaldomain.com[195.62.28.xxx]
Oct 16 15:44:17 mail postfix/smtpd[18600]: NOQUEUE: reject: RCPT from externaldomain.com[195.62.28.xxx]: 554 <localuser@localdomain.com>: Relay access denied; from=<user@externaldomain.com> to=<localuser@localdomain.com> proto=ESMTP helo=<server.externaldomain.com>
Oct 16 15:44:17 mail postfix/smtpd[18600]: disconnect from externaldomain.com[195.62.28.xxx]

here's my postconf
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
home_mailbox = Maildir/
inet_interfaces = all
inet_protocols = all
mailbox_size_limit = 0
mydestination = mail.localdomain.com, localhost.localdomain.com, localhost
myhostname = mail.localdomain.com
mynetworks = 127.0.0.0/8
recipient_delimiter = +
relayhost =
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_recipient_restrictions = permit_sasl_authenticated, reject_unauth_pipelining, permit_mynetworks, reject_non_fqdn_recipient, reject_unknown_recipient_domain, reject_unauth_destination, permit
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
virtual_alias_maps = hash:/etc/postfix/virtual

I'm using virtualmin to setup the mail accounts..
I can send mail for gmail for example and for the server email accounts.. but outside I cant send mails for my server email accounts..!