Hi to all! I've some problems with the Postfix SMTP server. I've disabled amavis and clamav following this steps: https://www.faqforge.com/linux/cont...ilter-and-antivirus-functions-in-ispconfig-3/ but it's not the problem. The server is: server2.opt-media.es The problem: SMTP Error (550): Failed to add recipient "[email protected]" (5.1.1 <[email protected]>: Recipient address rejected: User unknown in virtual mailbox table). I receive this error only when trying to send email to an external recipient @otherdomain.com but not all. I mean: The server is server2.opt-media.es and the MX record is even server2.opt-media.es. Wordpress contact forms are ables to send email either to local domain, to gmail but NOT to opt-media.net (and don't know how many others). Other rare problem, server is able to send emails from Wordpress, but not from Roundcube to the same recipient addresses. Like wordpress can send to [email protected] but the same address can't send outbound emails to himself, or to @gmail.com or to someone. No errors logged this time. MAYBE THIS CAN HELP? Think not cause my primary MX it's working: https://www.howtoforge.com/postfix_backup_mx I'm going crazy with that, it was working properly and perfectly. Now i encounter that error.