enable DKIM for relay-domains
when a complete domain is relayed there is no way to activate DKIM because a domain record may be created but must not be activated. To work around this I added a "and not exists (select 1 from mail_transport where mail_domain.domain = mail_transport.domain and active = 'y' and server_id = 1)" to the mysql-virtual_domains.cf. This works for me, because I only have entries of type @example.com in the relay recipients but must be probably check for the @ in the first place to work with single relay recipients.