You can no longer efile a 2018 tax return. Efile is available for the current tax year, 2019, only. The IRS requires that prior year returns be printed and mailed. You should be able to download a PDF of your tax return. This document can be emailed to another computer if necessary.
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E-filing for a 2018 return closed permanently in mid-October of 2019. The only way to file the 2018 return is by mail.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
Remember that federal and state returns must be mailed separately to separate addresses.