Interesting problem and not sure why this started happeneing about a month ago.

Problem.

If a calander request is send from any server outside my domain the meeting
request shows up as just a email in plain text and not a val meeting request.

I have tried to recieve meeting requestes from servers from other companies,
as well as a server i have in another domain and is set up exactly like mine.

When a meeting request is sent internally on my server it all shows up
correctly.
If i send a meeting request to the server in my other domain the request
shows up correctly
If a client in that other domain send me a meeting request i just get a text
email.

Both servers are running exchange 2003 sp1 and both clients are running
outlook 2003 sp2

Both servers are set to allow plain text and html formats, bot servers are
set up to use the exchange rich-text format ( determined by individual user)

icalendar is not enabled on either client, and both the internet formats are
set to defaults within outlook.

I double checked the default properties of the internet messaging formats on
both servers and they are the same.