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Inbound mail that carries a real classification. Open one to read both sides of the exchange and the record changes it produced.

These arrived and were written down, but no classification has been stamped on them: they predate classification, or the classifier has not run on them yet. Open one to see whether anything else touched the account.

Bounces and auto-responders. They are kept out of the reply count, which is not the same as being empty: an out-of-office often hands over a replacement contact or a new address. Each card reads its verdict off what the record captured, so it says nothing needed only when nothing was.