Hi all, As an extension of this topic with the same title: https://www.howtoforge.com/community/threads/soa-serial-number-format-is-invalid.76324/ I too am having this warning from MXToolbox.com: "SOA Serial Number Format is Invalid" I understand that the serial number should be a backwards date followed by 2 digits, ie: 2018080601 and ISPConfig appears to be doing this fine (see image), so why the error? I'm also getting some more errors which I do not know where to start looking: Reverse DNS does not match SMTP Banner - this has something to do with what my ISP is naming my public IP hostname, is that right? What should it be, exactly? What should the format be? 9.036 seconds - Not good! on Transaction Time - Why so slow? This is a fresh install with no load on the VM at all. At least one name server failed to respond in a timely manner SOA Expire Value out of recommended range - what effect will this have if it's 7 days or 14 days? Why the preference? Thanks in advance for your help!