How can I send meeting requests over the Internet? – Wayne Small

In order to send meeting requests to external organisations over the internet, you need to ensure that you can send MS RTF formatted messages to each other. You can configure RTF to send to that particular contact by changing the properties of the contact accordingly, or if it’s an entire organisation, you can modify your Internet Mail Service to force all mail to their domain into RTF format.
Be careful though, as users who are unable to read the MS RTF in Outlook you are sending them will end up with a winmail.dat attachment to their email message.