Sometimes Outlook 2007 is not associated with .eml files and therefore when downloading an email from Soup Mail, it does not open in Outlook. Typically it will try to open in Windows Mail or Windows Live Mail. The following registry keys need to be created/updated to fix the association:
[HKEY_CLASSES_ROOT\Microsoft Internet Mail Message\shell\open\command] = "%ProgramFiles(x86)%\Microsoft Office\Office12\Outlook.exe" /eml "%1"
[HKEY_CLASSES_ROOT\Microsoft Internet Mail Message WLMail\shell\open\command] = "%ProgramFiles(x86)%\Microsoft Office\Office12\Outlook.exe" /eml "%1"
See attached registry files that can be downloaded and run (as an Administrator) to update the settings. Note that you must choose the file that relates to your version of Outlook (2003 or 2007) and the bitness of Windows (32-bit or 64-bit):