I think this is a scam to get your cc info. There is no such redeposit fee.
I recently left my kindle on a UA plane and reported it to lost and found. I received a very similar signed email from a "united employee" asking for my cc info so they could FedEx the kindle to me. Everyone I showed the email to (including FedEx) said it was a scam.
I reported the incident to UA, and they deposited 10K miles into my account, not understanding the bigger issue of "employees" trying to gain access to cc info.
UA could have a bigger problem here and I hope UA Insider sees this thread.