From chapter 13 of Programming and Problem Solving with C++, page 715 5PP

5. You've gathered lists of email addresses from a variety of sources, and now you want to send out a mass mailing to all of the addresses. However, you don't want to send out duplicate messages. All of the email addresses (represented as strings) have been combined on a single file called rawlist.dat. You need to write a program that reads all of the addresses and discards any that have been previously input. Use one of the list classes from this chapter, modifying it as necessary to work with string data, and to deal with as many as 1000 items. After all of the data have been read, output the new mailing list to a file called cleanlist.dat