What cannot be purchased using a credit card at the post office?

The correct answer identifies that COD (Collect on Delivery) funds and trust fund deposits cannot be purchased with a credit card at the post office. This is due to specific regulations governing these services, which require payment through alternative methods. COD funds are used by the recipient to pay for a parcel upon delivery, and the handling of this transaction is managed differently, often necessitating cash or a bank draft for security reasons.

Additionally, trust fund deposits often involve government or other institutional funds that have strict protocols surrounding their payment processing, which also excludes the use of credit cards.

In contrast, items like stamps and services related to money orders or international shipping are generally available for purchase with a credit card. This makes it important for customers to be aware of the types of payments accepted for different postal services, especially those that involve sensitive transactions such as COD or trust funds.