assitance in problem with relay of email on linux PostFix

Ubuntu 12 linux, Virtual-WebMin PostFix Dovecot on Ubuntu 12.04 the mailserver id ok.I I have domains like [login to view URL] and users for mail like I use roundcube for webmail . it works fine. Sending mail tp [login to view URL] works. now i try to use the account from a different mailclient like Outlook or Mozilla Thunderbird. i can send and receive emails to domains registered on the ubuntuserver as virtual servers. i cannot relay emails to a different domainname like gmail.com. response of the mailserver is: 5.7.1 Relay access denied. there is a postfix/[login to view URL] : smtpd_relay_restrictions = permit_mynetworks reject_unauth_destination permit_sasl_authenticated smtpd_recipient_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination I followed most forums in askubuntu and virtualmin with no result.