Someone who uses Netscape 7.2 for email reported that the count for unread messages, which appears on the left hand side of Netscape's mail window, was showing uread messages, but he couldn't find them. When I checked his system, I found he had changed the message "view" to show only messages with attachments. I changed it to show all messages again, by selecting "All" for "View" ("View" appears slightly above the list of messages in a folder).
Netscape 7.2 supports the following "views"
People I know
Last 5 Days
There is also an option to customize the view of messages.