收件人地址被拒绝：虚拟邮箱表中的用户未知;

I have centos with postfix in plesk. I have setup a domain and when I send email to the same domain from within webmail the email delivers correctly. When I send email outside of the listed domain to say a work address I get the above error. Its as if the machine tries to deliver it locally, cant find the domain so throws an error. Shouldn't it deliver the email to external mail systems as well?I have centos with postfix in plesk. I have set