Fannie Mae (FNMA) is a service that facilitates mortgage loans by both purchasing and guaranteeing them, though it does not directly provide mortgage loans. Banks will process FNMA loans which are then underwritten by the bank but guaranteed through FNMA. FNMA handles foreclosures for these mortgages and consequently may end up managing some of these properties, but otherwise FNMA is not directly involved in the lending process.
As a government enterprise, FNMA provides services to make it easier for both homebuyers and investors to purchase properties. This includes a number of credit options and loan modifications. FNMA will require a tax ID (either an EIN or an SSN) from the buyer, but because FNMA is not a product in and of itself, its products do not require EINs or SSNs. FNMA itself has its own identifying tax ID number. Buyers who have EINs, SSNs, or ITINs will be able to put in an application for FNMA-backed loans, but again, the loans are not delivered by FNMA.