Upgraded to Windows 7. I use Outlook 2007 for email. When sending email to some of my recipients, I receive an email from System Administrator that email is undeliverable to following recipients; does not list the recipient or give the reason. I chatted with my Internet Provider and they said it is because Windows 7 does not support Outlook however, Windows 7 indicates Outllook 2007 is compatible. This only happens with random email addresses, not all of them.