I currently have Postfix running on a box that also hosts a number of websites. Although the website domains' DNS all have an A record pointing to this server, the server has no hostname of its own. The Postfix is used for outgoing SMTP only; incoming is handled by Google Apps. All outgoing mail is signed by OpenDKIM, and SPF is enabled as well.
The question is, does the server needs its own hostname, especially for Postfix? I've heard conflicting advice about whether Postfix needs to have a real FQDN set for myhostname/mydomain to prevent messages from being classified as spam.
So far, I do not seem to be experiencing any issues with a default 'server.localdomain' hostname. Is it OK to keep using this, or should I look to get a real domain just for the server?