About two to three weeks ago two of our Outlook clients started
receiving Calendar Appointments from external users as emails rather
than appointments. Internal appointments are working fine, but
appointments from external senders arrive as HTML mails rather than in
appointment format.

What makes this stranger is that it's not consistent. Originally it
was two users, but now more users are reporting the same behaviour.
It's really convenient to get external appointments that you can
respond to - does anyone have any ideas / fixes or has experienced the
same problem.

We're using Windows SBS 2003, XP / Vista, and Outlook 2003 / 2007.
Everything is patched to the latest SP. We use Trend CSM 3.6.

(I looked hard for a recent posting on this issue but haven't come
across anything. Apologies if this is answered elsewhere.)

Thanks,
Phil