By default SMTP Express uses the FQDN assigned to the computer itself.  However, you can make a change in the registry to have a different FQDN added to the email headers. To change the registry, do the following:

1. Launch Regedit by choose Run on the Windows start menu then entering "Regedit".
2. Expand the following item:
   HKEY_LOCAL_MACHINE\SOFTWARE\Quiksoft\EasyMail SMTP Express
    
3. Right click and select New String Value.
   
    
4. Enter a name of HostName.
5. Now double-click on HostName and under Value Data enter the FQDN you wish to use.  For example:
   
   myserver.somedomain.com