This issue only happens when downloading email via POP3. If you do not actively choose to delete emails from your mailbox once you download them, the emails will stay on the server and will be downloaded again the next time you download your email.
This is not something to be that concerned about, but you may have an issue down the line when your mailbox reaches its limit.
We do recommend that you use IMAP when downloading your emails, as all major email clients support it and it will remove the emails from your mailbox.
If the storage on your mailserver is ever restored from a backup, mail that might have already been downloaded from the server may be in the backup and will be re-downloaded. This is nothing to be concerned about, but you should raise a Support Ticket with the Customer Services team to ensure that the backup has run smoothly.
Article ID: 257
Created On: Fri, Mar 13, 2015 at 11:50 AM
Last Updated On: Thu, Apr 23, 2015 at 11:36 AM
Online URL: https://www.heartinternet.uk/support/article/why-is-my-mail-client-downloading-duplicates-of-existing-emails.html