Cannot receive emails in desktop client after migrating email account between cPanel servers

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http://serverfault.com – I have a cPanel account whose emails I migrated from another server. The account can receive emails in SquirrelMail but cannot receive emails in Mail.app on OSX. I can test the account with Outlook's test button successfully, though I've not tried to download any emails. The chances are, a brand new account would work correctly. I need to find a way to import those existing emails from the old server into the new server and have the accounts work properly. To migrate the emails, I copied the mail directory from the root of the old cPanel account and uploaded that to the root of the new cP (HowTos)