This has just popped up for one of my users. Nowhere in AD can I find the duplicate. But when an outside user sends mail to one of my users they get the error: "A configuration error in the recipient's e-mail system prevented delivery of this message. Two recipients are configured with the same e-mail address. contact your administrator." I've never seen that before and I didn't think it was possible in AD to have two objects with the same e-mail address. Anyone have any clues?