A Proof of Sources of Funds (POSOF) is any (collection of) document(s) that explains where the funds used for a fiat deposit originated and where the crypto assets used for a fiat withdrawal originated.
Kraken may request a proof of source of funds for clients based in the United States depositing and withdrawing USD via domestic United States wire transfers.
Kraken reserves the right to ask any client using any funding methods for a POSOF.
Any POSOF document submitted needs to cover all deposits or withdrawals via that particular funding method. If a client has made deposits or withdrawals earlier they should make sure that the POSOF documentation covers any previous deposits or withdrawals as well as the most recent one.