I thought that you might be able to create a rule in the Server config|Router/SMTP|Restrictions and controls|Rules section. The options available don't allow you to tag the message though.
Then I thought you might be able to use attention indicators to change the backgroud color of messages but I don't think this is supported in DWA.
Lastly I was thinking you could possibly modify the mail template which may be more work than you intend as modifying the DWA side of the mail template can be tricky. It may be on option though.
Hope this helps.
Feedback response number WEBB7PJ6VU created by Michael Millar on 02/22/2009