Open the configuration file of Postfix server /and many others/postfix/most important.cf and change smtpd_recipient_restrictions option and include the following selections such as this: Just after installing the Postfix mail server, you must configure it; you will find the vast majority of its configuration documents beneath the /etc/postfix/ Listing. Until Google https://www.hostscheap.com/business-email-server-setup-service