No. By using POP, all of your messages have been saved to a file on your hard drive, and you will have continued access to them via your email program. Also, it is very easy to incorporate these messages into your new IMAP setup, and store them back on the email server. Most major email programs have the option to import messages from a POP account, or an archived data file, to an IMAP account. Some programs with graphical interfaces will also allow you to drag your messages from locally stored folders and drop them into IMAP folders on the server.