What will the IRS do in the event that I filed twice — I both e-filed and mailed in return(s)?
If you’ve already e-filed, you shouldn’t also send a mailed return.
If both returns were the same and the IRS already accepted the e-filed return, the IRS will reject the return that you mailed. However, the rejected return might delay the time it takes the IRS to process your return. It also might take longer to receive your refund if you are owed one.