That's how I got in trouble the first time: changed the accounts as recommended and went from small number to over 30,000. However, I believe a fix for my email timing out may be a logical fix for this problem. Go to your email provider and log in. Make a new folder called Temp or something. Move all of your regular emails in the inbox to Temp. You may have to do this screen by screen as my provider att.net would only let me move 50 at a time.
Go back into your email and delete all of your emails - original and duplicates. This will delete everything but since there is nothing in your provider's inbox, nothing will be deleted there. Close your email. Go back to your provider and move the emails from Temp back to the inbox.
Go back to your email and download your emails. Your inbox is empty and only the emails from your provider inbox will download. The only problem is that any emails in your other folders will be downloaded again into your inbox. I don't know but someone may have an answer. If you delete the duplicate emails from your inbox that you have in folders will the emails in folders disappear. I don't think so but I'm no expert on Live Mail.
CAUTION: Some one who has a small email account should try this out first to verify that it works. I know how files and folders work and in gmail, folders are only labels and when you move or delete an email, just the label changes and the email shows up in the appropriate folder.
Jim