Yes, you do need to mail your supporting statements, such as your brokerage statements (Form 1099B) and Form 8453, but you don't need to include Form 8949 since TurboTax filed this form electronically with your tax return. You can include it for reference purposes, if you like.
It's always a good option to send documents to the IRS by a method that provides tracking information.
Note that you must postmark this mailing no later than three days after your e-filed return is accepted by the IRS.
Why do you need to mail Form 8453?
When you use the summary method, TurboTax only produces a Form 8949 with the summary totals that you entered, not the individual transactions, so Form 8949 that is included in your e-filed return is NOT sufficient for this purpose. Thus, to satisfy the requirements of utilizing summary reporting, you need to mail Form 8453 to report the details of your transactions per brokerage statements Form 1099Bs.
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