I'm getting annoyed that I'm receiving true duplicate messages from a
couple vendors. Same message-ID and everything, and there's no way in
Outlook to automatically check the message-ID of a message as it comes
in and delete it if it's a duplicate message-ID.

so im looking for it all.
is there, forgetting price, a good web-based/interfaced outlook calendar
program.  so various users can enter on their computers, then have it
synchronized to all calendars.