Problem with emails that are graylisted

I am not sure I understand what Graylisting is but the problem I am having is that I have emails that are gray listed but when I look at the exchange server queue, I do not see anything in queue for delivery.  Yesterday I had to restart the information store and suddenly I got several emails that were gray listed back as NDR.  My guestion is where were they stored if they are not in the queue on exchange.  Any help would be appreciated.
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Reid PalmeiraTelecom EngineerCommented:
they're actually stored on the source MTA, not onr your target exchange server. short version is that graylisting works by sending a busy message to the sender, so the messages aren't in your queue unless the address is whitelisted.

see: for a better description.

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Reid PalmeiraTelecom EngineerCommented:
cheers, thanks for the pts. and grade. hope that helped.

Will fix problem with graylisting and Exchange 2003 SP2
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