The FOA (Form of Authorization) is an ICANN mandated message (basically an Email template) that the registrar needs to send to the “registered name holder” when an incoming (gaining) or outgoing (losing) transfer request is received.
The gaining side FOA is used in order to obtain the registered domain holder’s permission in order to transfer a name from another registrar to yours. The losing side FOA is used when another registrar has requested a transfer out for a domain that was previously held under your registrar. While the transfer out is auto-completed after five days. this gives the domain holder another chance to review the transfer that is going to happen to make sure it is happening with his knowledge.
The emails form part of the Inter-Registrar Transfer Policy (IRTP).