You fail to mention if either you or the receipient are using an Exchange
server, and if you both are part of the same one.
Are you part of an exchange server group or are you working from your
home/small office as a standalone user of Outlook?
If you are using thsi behind an exchange server, do all receipents get the
same result, or is this only for those people outside of your organization?
If you are a standalone user, do both yourself and your intended recieients
have some sort of an iCalendar account?

"Osnat Farouz" wrote:

When I send a meeting request the recipient does not receive it as a meeting
request but as a regular mail. In Outlook options, the option "when sending
meeting request over the internet, use iCalendar format" is checked.