I discovered that my DSL provider also provides domain with static IP: from nslookup: Can I use this domain for "technical domain"? If so, what should I use for hostname instead server1.example.com, server1.bsn-xxx-xxx-xxx.dsl.net is of course not resolvable. What should I use in /etc/postfix/main.cf and ispconfig? Can I use just bsn-xxx-xxx-xxx.dsl.net, without server1?