Too Big to Fail banks are a blight on our economy. They are too big because if they fail, their depositors (individuals, businesses, and governments) will lose more money than can be covered by deposit insurance. They got too big because there are no alternatives except local banks and credit unions that have limited presence on a national scale.
Companies such as Wal-Mart are already offering deposit-only banking services for reasonable fees. The USPS already has the core competency to provide such a service. Its existing physical infrastructure would be second to none in providing for national banking.
A deposit-only Postal Checking Account service would provide a safe place for peoples' money so the big banks could be wound down until they can do no more harm.