How to combat ticket duplicates that may appear in your helpdesk.
First of all, please make sure that you've got no duplicates are in the mailbox. Sometimes duplicates are caused by messages sent as copy to another address that also forwards to the support address, e.g. when you Cc: to an email group that includes the helpdesk address.
Next, please see if the duplicates are identical. If the body of the duplicate tickets is different, that's a sign that the duplicates have been created by users who have been CC'd in the message sent to the helpdesk, who have replied-to-all when sending a reply to the message. In this case, just tell your users to use the regular reply instead of replying to all.
Make sure the messages are deleted from the mailbox (or marked as read) after they are retrieved. If any messages remain (unread) in the mailbox after the mail has been checked by the helpdesk, try deleting the messages manually. If the server is set to keep the messages that have been retrieved via POP3/IMAP, consider clearing that settings – the messages must be deleted from the support mailbox once they have been retrieved.
Finally, duplicates might occur if the connection between your application and the support mailbox is slow. Consider placing the mail server in the same network with your web server (if you host them locally) or consider using a faster email service provider, e.g. GMail.
Hopefully these recommendations will help you resolve the issue. If you have tried everything but still need help, please don't hesitate to contact our Support; we'll take a closer look at your specific case.