Now we are using exchange 2010 upgraded from Exchange 2003, people are using meeting invitations & scheduling. These work well when sent internally, people can accept, decline or tentative as they should, but when the go outside the organisation the invitations are sent as a blank email (see screenshot attached).
I have unchecked the calandar option "send in Icalandar format", that doenst work
I have cleared the outlook cache, that doesnt work
Emails are sent in HTML format or RTF & neither work