Fitch Rates IndyMac MBS $240.9MM RAST Series 2005-A3.

NEW YORK -- Fitch rates IndyMac MBS, Inc., Residential Asset Securitization Trust (RAST) 2005-A3, residential mortgage pass-through certificates, as follows:

-- $240.9 million classes A-1 through A-4, PO, A-X, and A-R ($240,902,285 senior certificates) are rated 'AAA'.

The 'AAA' rating on the senior certificates reflects the 4.50% subordination provided by the B1 through B6 certificates, which are not rated by Fitch. Fitch believes the above credit enhancement will be adequate to support mortgagor defaults, as well as bankruptcy, fraud, and special hazard losses in limited amounts. In addition, the ratings reflect the quality of the mortgage collateral, the strength of the legal and financial structures, and the capabilities of IndyMac Bank, FSB (IndyMac) as master servicer (rated 'RMS2+' by Fitch).

The mortgage pool consists of 1,383 recently originated, conventional, fixed-rate, fully amortizing, first lien, one- to four-family residential mortgage loans with original terms to stated maturity of 30 years. As of the cut-off date (March 1, 2005), the pool had an aggregate principal balance of approximately $252,254,560. The average loan balance is $182,397, and the weighted average original loan-to-value ratio (OLTV) for the mortgage loans in the pool is approximately 68.86%. The weighted average FICO credit score for the pool is approximately 712. Cash-out and rate/term refinance loans represent 39.30% and 23.65% of the pool, respectively. Second and investor-occupied homes account for 2.10% and 13.74% of the pool, respectively. The states that represent the largest geographic concentration are California (33.78%), Florida (8.11%), and New York (7.80%). All other states comprise fewer than 5% of properties in the pool.

None of the mortgage loans are 'high cost' loans as defined under any local, state, or federal laws. For additional information on Fitch's rating criteria regarding predatory lending legislation, see the press release 'Fitch Revises Rating Criteria in Wake of Predatory Lending Legislation,' dated May 1, 2003, available on the Fitch Ratings web site at www.fitchratings.com.

The loans were originated or purchased by IndyMac Bank, F.S.B., which it subsequently sold to IndyMac MBS, Inc. IndyMac MBS, Inc. deposited the loans in the trust, which issued the certificates, representing undivided beneficial ownership in the trust. For federal income tax purposes, elections will be made to treat the trust as separate multiple real estate mortgage investment conduits (REMICs). Deutsche Bank National Trust Company will act as trustee.