Outlook 2013 has duplicate emails and tons of unread messages

I recently installed 4 new PCs--all are Windows 8 professional. All 4 have Office 2013. Issue 1: users are getting duplicate emails. I think I have resolved this by unchecking "keep email on server for 14 days" in advanced settings section. They use POP email with their ISP (CenturyLink). Internet connections have been intermittent over the last 10 to 14 days, coinciding with the occurrence of this problem so I think this will minimize the issue--agree or disagree? They only have one email account, only one email address each.

Issue 2: This one I can't understand; Friday when they left they had minimal unread messages in their Inboxes--now this morning they have multiple folders with tons of unread messages, some going back to April 2013 and others as far back as 2012. Have no idea what can cause this--I do know if you import emails (which I did 2 weeks ago) you may get a bunch of emails showing up as unread but can't explain how Friday all is OK, then this morning hundreds of unread emails. Any ideas, suggestions? Thanks.
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Lionel MMSmall Business IT ConsultantAsked:
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Issue 1:
You are correct, this happened because of the option "keep email on server for 14 days" but you do not have to uncheck it now. When it finishes with all the mail it will stop by it self

Issue 2:
Probably all the old emails have been downloaded again

This normally won't happen again, only if you change pc
Lionel MMSmall Business IT ConsultantAuthor Commented:
Thanks for that but it was actually a bad electrical socket--the DSL modem kept losing power and internet connections--which explains issue 1. As far as issue 2 goes your suggestion can't work because the server USED TO store only 14 days of emails. emails that showed up as un-read where as far back as April 2012--we have dealt wit this but clicking on the folder and converting all email to "read". So we have removed the issue but do not know the cause.

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Any news?
Is everything ok now?
Lionel MMSmall Business IT ConsultantAuthor Commented:
Problem went away when we changed the electrical outlet
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