If you have the VPOP3 In Mail setting Leave Mail On Server enabled, then VPOP3 will leave your messages on the ISP POP3 server for the specified number of days after downloading it.
If, during this time, you want to make VPOP3 download those messages again, then you can do so by following the procedure below.
Note that you cannot selectively download messages again using VPOP3 (there are other utilities available on the Internet to do this) - you have to re-download all the left messages again. Procedure
If you just wish to download a few messages again, you can avoid disruption to most of your users by using the following technique.