Outgoing E-Mail header shows Received: from jacky.localdomain

[Skylinux]

I have a problem with my ISPConfig CentOS 5 server. All E-Mail I sent out have "Received: from jacky.localdomain (111-222-333-444.slicehost.net [111.222.333.444])" in their header.

Where 111.222.333.444 is the correct IP of my server.
Where do I need to go to configure the correct hostname? I have checked the ISP configuration panel and my settings are:
Hostname: jacky
Domain: MyRealDomain.org
IP Address: 111.222.333.444
Netmask: 255.255.255.0
Admin Email: admin@MyRealDomain.org

Thanks

[Skylinux]

I ran

postconf -e 'myhostname = jacky.MyRealDomain.org'
postfix reload

and all appears to be well now, I will know more once I reboot the server tonight.....