Your shipping account is used to pay for the postage you purchase, which helps us minimize how many times we charge your credit card (we know how annoying that can be!). While the minimum balance is $25, you can choose to add more funds to cover the entire week or month of shipments and further minimize charges to your card.
In addition, USPS reserves the right to re-weigh or re-measure a package, and may (on rare occasions) assess other charges after the package is on its way, such as a redelivery fee after a certain number of attempts. These are typically called assessorial charges.
We maintain a minimum balance in your shipping account to handle these charges immediately. Otherwise, your shipment could be held by USPS until we can reach you and secure payment, and no one likes delays in shipments! This way, your package isn't delayed or returned. We let you know immediately about the additional charge, and you also have a clear record of all charges on your account page.