If you do not have your spouse's social security number and are trying to file married filing separately, you will not be able to e-file because the IRS requires married people filing either MFJ or MFS to provide both spouses SSN when e-filing. The only way around this is to file MFS and paper file your tax return. When you have finished the Review phase of your tax return preparation, select File and choose File by Mail instead of E-file. Then you will print, sign, date, and mail in your tax return.