spondee wrote:

And how would that cause duplicate emails??? Or prevent them?

When a message arrives, Outlook applies each rule in turn to see if the
conditions match. Supposed a rule's condition matches a message and that
rule caused the messages to be moved to a folder. Outlook does so. Now, if
the "stop processing more rules" action is not on that rule, Outlook retains
the original message in the Inbox and continues with the next rule to see if
its conditions, too, match. This continues until all rules have been
processed. Outlook stops processing, but you now have a copy left in the
Inbox in addition to the one that was moved. If, instead, Outlook had seen
the "stop processing more rules" action on the rule that matched, Outlook
ended processing at that point and would have deleted the Inbox copy because
the rule said "move" and you would not have a duplicate left over.
--
Brian Tillman