If you get duplicate messages when VPOP3 downloads mail from the ISP there are several common reasons for this:

If your ISP gives you one POP3 mailbox for each VPOP3 user, then you have to tell VPOP3 which user each mailbox is associated with. If you don't do this, then when a message is sent to two VPOP3 users, each user will receive two copies of that message.

To link each ISP mailbox with a VPOP3 user, go to the VPOP3 Mail Connectors → Mail Collectors page. Then, for each Mail Collector you have, in the POP3 Routing tab, choose Send all messages to a specified user/list and select the VPOP3 user who this POP3 mailbox is for.

If VPOP3 gets disconnected when downloading mail from the ISP and you do NOT have Leave Messages on Server for X days enabled on the In Mail tab in VPOP3, then the next time VPOP3 connects it will download all the messages again.

This is because, although VPOP3 has asked the ISP to delete the message from the ISP POP3 mailbox the POP3 standard says that if a connection error occurs, the ISP must automatically undelete all messages which were deleted during that session.

The solution is to tell VPOP3 to Leave Messages On Server for at least one day.

Check that you do not have multiple identical Mail Collectors defined in VPOP3. If you do,then remove all but one of them.

Using the Processes list in Windows Task Manager, make sure you do not have more than one copy of VPOP3.EXE running. (Click on the Show Processes for all Users button/box if there is one).

If none of these common causes matches your problem, then you need to send a copy of a set of duplicated messages (eg if you receive two copies of a message, send both copies) to support@pscs.co.uk with any other information you have (eg which messages are duplicated etc). We must see the FULL message headers, not just the abbreviated headers which many email clients show by default.