From Brana Bujenovic:
Delete Duplicates for Eudora enables you to detect and delete duplicate e-mail messages from your Eudora mailboxes. It is a plug-in, i.e. an auxiliary program that interfaces with Eudora (for many people the e-mail software of choice), can operate in and on the Eudora environment.
A variety of conditions, ranging from mail server errors to events that occur on one's own computer -- such as explicitly copying messages via a Eudora mail filter, moving or copying and amalgamating mailboxes, especially in moving files from one drive to another or one computer to another, restoring backed up mail files, and so on -- can lead to the presence of duplicate mail messages. While some people may not care about these, anyone who either likes having an organized filing system or being able to keep track of whether messages have been responded to or appropriately handled will find such duplicates a nuisance, aside from the fact that they waste space on one's hard drive, especially when it is a question of not only one copy of a message but multiple copies. When you add to this the condition that multiple copies of a message with an attachment lead to multiple attachments, and that messages with embedded graphics, which are an ever larger portion of Internet e-mail, store multiple copies of these graphics files, we are talking about a potentially large mess.
Fortunately, Delete Duplicates for Eudora will solve this problem and help you maintain an ordered mailbox and message system by eliminating duplicate messages, attachments, and embedded graphics, under a variety of conditions and according to a variety of user-selectable and configurable options. This will enable you to keep your Eudora mail in the kind of order that makes the most sense for the way you prefer to conduct your life, your profession, or your business.