How can I configure myhostname to work with Postfix?

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http://serverfault.com – I'm going through the process of setting up a Discourse forum on my server (Ubuntu 12.04 x64) and am getting stuck at the point where I have to configure mailers. I'm following Discourse's instructions and am stuck trying to configure postfix for Mandrill. It is says to check my fully-qualified domain name by typing hostname -f When I enter in hostname -f, I get localhost. As far as I know, entering in hostname -f should return mydomainname.com. When I just enter in hostname, I get mydomainname which is correct because that is what I set my hostname to in /etc/hostname. Looking at some of (HowTos)