[ubuntu] What should Postfix System Mail Name be?

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http://ubuntuforums.org – I have a virtual server with a static IP and a real FQDN. I set up Postfix on it and everything works. While setting up Postfix, the guide that I followed suggested that I enter the server's FQDN as Postfix system mail name which I did (My FQDN and reverse DNS given to me by my hosting company is something like virtualhost123.myhostingprovider.com). Now I want to host two domains on this server: say domainA.com and domainB.com. When I send outgoing mail to Gmail from my server for example (let's say from e-mail address [email protected]) everything works fine but in the e-mail received, G (Hardware)