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This has never happened to any other customer so far and even we use out pop3 accounts in outlook. I am not sure what settings you have in your outlook as this is something which I have never seen while using pop3 accounts.
Also check if you have gone through following procedure or not :-
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1)Open Outlook.
2)On the Tools menu, click Accounts.
3)Click Add, and then click Mail
4)Type Your name in Display name as you would like it to appear.
5)Type your email address people use to send email messages to you.
6)Type newnetters.co.uk under incoming mail(POP3, IMAP OR HTTP) server as well as under Outgoing mail SMTP server.
7)Follow the instructions as above in the Internet Connection Wizard until you reach the Internet Mail Logon page

In Account name, type your POP3 service user name, followed by the domain, for example, someone@ newnetters.co.uk.
In Password, type the password associated with your POP3 service e-mail account.
9)Click on properties button.
10)Enable: My servers requires authentication in servers tab
11)Enable: Leave a copy of message on the server in advanced tab.