Multiple old emails are downloading again automatically in outlook

[siva N]

I received porblem from my client ,She accessing her emails in outlook 2013 app and the account type is pop3.Whennver she open the outlook, the old emails which means the readed emails are downloading automatically.

What i tried and reviewd on this issue,

I have treid to reconfigure user outlook profile but the issue still persist

User acceessing and saving her outlook .ost from NAS share and she has the archived PST file on smae share but those are saved in different folders.

This is issue only for specfice user not for all, so this issue happening on outlook or user workstation. Could you please advise what is the casue of this issue and how to fix this

[#2]

By "reconfigure user outlook profile" did you make a brand new profile for her?
What is the email system that Outlook is connecting to?
This kind of sync issue is often due to a corrupt message in the Pop mailbox. Can she access the mailfile another way (eg web browser login to the mailbox) and delete a few of the oldest emails that are duplicating?