[defanor]

Yes, and I've actually never used Outlook with Exchange. But I'm only sending plain text responses, not trying to use any advanced features, and it works fine to receive and read meeting invites (just as messages).

What goes wrong with plain text responses in Outlook, by the way?

[simplect]

Outlook uses small fonts to render the response and there is a noticeable gap in readability between HTML formatted and plain text responses.