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When I click “Subject” I would expect that the yellow items are grouped together. The replied mails should be in the same group as the original mails, even if they have the prefix “Re:” or “Fwd:” in their subjects.
Figure: The yellow items should be in the same group
And other ones along the same lines – these 3 should be together
Figure: Screen capture from Outlook 2003 Beta 2
Figure: Outlook won’t thread the two messages together