As a self-custodial wallet, when you hold native XRP it is held directly on the XRP ledger. The XRPL has its own functionality and requires that all addresses must hold at least a minimum balance. This required reserve amount varies with updates to the ledger, however at the time of writing it is 12 XRP.
At a 12 XRP reserve balance requirement, this would mean that if you receive 100 XRP, you would only be able to send 88 XRP out. However you would be able to send out the full amount of any subsequent receipts.
Due to the XRPL minimum balance requirement, you also cannot send less than the reserve amount to a new XRP address.
