I am looking for an Applescript to mark messages as read within Outlook 2011 for Mac.
I have not been able to identify the correct property to set.
The above answer is great, if you want to select the message(s) to mark as read. but with Outlook on Mac putting Calendar invites in Deleted as "unread"...this version will run for you and can be set up to do it's thing from cron as often as you would like.
tell application "Microsoft Outlook"
repeat with afolder in deleted items
set aMsg to (every message of afolder where its is read is not true)
repeat with aMessage in aMsg
set aMessage's is read to true
end repeat
end repeat
end tell