MBS Investor MBS InvestorFor MBS Mortgage Loans, either a Third Party MBS Investor for Lender-Arranged Sales, or the Multifamily Trading Desk. for an MBS Mortgage Loan MBS Mortgage LoanMortgage Loan purchased by Fannie Mae in exchange for an issued MBS backed by the Mortgage Loan. , or Fannie Mae for a Cash Mortgage Loan Cash Mortgage LoanMortgage Loan purchased by Fannie Mae in exchange for cash. .