As far as i know ISPConfig sends admin mails with the admin email address in the FROM Header. Let's assume it's [email protected] example.com. If there's an SPF and DMARC Record for example.com that prevents sending mails from non authorized IPs, then the mail would not be deliviered. You would have to add every server ip to the SPF Record in order to allow sending mails, which would be a bad workaround (?). Is there a way to configure the sender email-adress of the admin mails to something like [email protected] hostname.com ?