Rule to assign Category causes email appear "read"

[zolist]

I have rules to assign categories based on keywords and sender domain
min Outlook 2003. New mail gets "lost" however, as processing these
rules causes the email to have the "read" flag, so I don't see the new
email counter in the relevant folders. Other rules (move, forward) do
not have this side-effect, only assigning a category.
Is there a way to prevent this or have a rule to turn the email
"unread" again?

Thanks,
Z.