Hello, I set up Relayhost for SparkPost on ispConfig mail server, Sending domain on SparkPost, opended port 587 on the firewall and DNS records. When I try to send I get this error:The mail system <firstname.lastname@example.org>: host smtp.sparkpostmail.com[18.104.22.168] said: 550 5.7.1 relaying denied (in reply to RCPT TO command) Reporting-MTA: dns; web.zix.is X-Postfix-Queue-ID: 664FE2192A X-Postfix-Sender: rfc822; email@example.com Arrival-Date: Mon, 29 May 2017 17:32:26 +0000 (UTC) Final-Recipient: rfc822; firstname.lastname@example.org Original-Recipient: rfc822;email@example.com Action: failed Status: 5.7.1 Remote-MTA: dns; smtp.sparkpostmail.com Diagnostic-Code: smtp; 550 5.7.1 relaying denied Is the problem names on server web.zix.is / mail.zix.is ? I'm using mail.zix.is in SendingDomain on SparkPost. Should I use DKIM record from Sparkpost or the one ispConfig generates in the DNS ? How to fix ?