Many find the easiest way to figure the entries for Form. X is to first make the changes in the margin of the return they are amending.You can now file Form 1040X electronically with tax filing software to amend your Form 1040, 1040SR, or 1040NR for the current or two prior tax periods. You can find the CP or LTR number on the right corner of the letter. To claim a refund, you must file an amended return within 3 years after the date you filed your original return or 2 years after the date you paid the tax. Most IRS letters and notices are about federal tax returns or tax accounts. Welcome to MassTaxConnect, the Massachusetts Department of Revenue's web-based application for filing and paying taxes in the Commonwealth. The primary letter we use to request information about a return is Form DTF948 or DTF948O, Request for Information (RFI). This letter provides proof that the IRS has no record of a filed tax Form 1040, 1040A or 1040EZ for the year you requested. The Commonwealth follows IRS rules when generating these forms.