What is the ruling on depositing money in the post office or bank while taking interest, and what is the difference between the two?

Depositing money in the post office or bank constitutes a usurious loan that is forbidden, as the owner of the money lends it to the post office or bank in exchange for interest. This differs from a legitimate deposit (wadi'ah shari'yah), which is a trust (amanah (definition)) whose ownership does not transfer and from which the custodian does not benefit. The bank or post office disposes of these funds and is obligated to return their equivalent. It guarantees them, whether there is negligence or not, and this is the reality of a loan. Any interest thereon is forbidden usury (riba).