Hi, I'm running a Ubuntu 14.04 mail server and I installed opendkim. For the domains I create the DNS TXT record for dkim the mail header says dkim=pass (1024-bit key) header.d=maildomain.si Received: from mail.serverdomain.si ([127.0.0.1]) but on domains that I don't create the record it trys dkim but does not work dkim=neutral reason="invalid (public key: not available)" header.d=maildomain.si Received: from mail.server.si ([127.0.0.1]) I have configured my /etc/opendkim.conf Domain * KeyFile /etc/postfix/dkim.key Selector dkim SOCKET inet:[email protected] # Common settings. See dkim-filter.conf(5) for more information. AutoRestart yes Background yes Canonicalization relaxed/relaxed DNSTimeout 5 Mode sv SignatureAlgorithm rsa-sha256 SubDomains no #UseASPDiscard no #Version rfc4871 X-Header no Added few lines to postfix main.cf and added no_milters to receive_override_options in master.cf. milter_default_action = accept milter_protocol = 2 smtpd_milters = inet:localhost:8891 non_smtpd_milters = inet:localhost:8891 Then created the key with opendkim-genkey -t -s dkim -d * And added the DNS TXT record Hostname dkim._domainkey.domain.si. Text v=DKIM1; g=*; k=rsa; p=<the content of the key> Now I wonder: 1. Does the ispconfig install and clients mail domains count as a multi domain mail server? 2. Do I need to create a rsa key for every clients mail domain? 3. Can I create a rsa key just for my servers FQDN and use it for all or is there a way to create 1 key for all (like the startls cert that i use for all domains)? 4. Any other advice?