Why can't I move large emails from one mailbox to another on Exchange 2010?

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http://serverfault.com – I'd like to move some emails from one mailbox to another. I have both mailboxes accessible in Outlook 2010. All emails have moved successfully except a couple that are >20mB, for those I receive: Cannot move the items. The item cannot be moved. It was either already moved or deleted, or access was denied. Since it's just the larger emails that won't move I keep looking toward limits as being a culprit, except there aren't any set. The recipient mailboxes are set to use database defaults, and the database storage limits remain off. (Since they're off I haven't changed them, but I'm aware (HowTos)