The web site for domain yyy.com is on an ispconfig server (centOS). The domain email accounts are on another server. Mail from a form (PHP) will not be delivered to this domain (yyy.com) but will be delivered to all other addresses. The log entry is: <email@example.com>: Recipient address rejected: User unknown in local recipient table I set the domain to use an External Mail Server but it still does not send the messages. I don't think that I can put the same address on this server since it exists on the other. Is there a way for mail addressed to firstname.lastname@example.org to be delivered?