No version of Turbotax can mail your return for you because you have to print and sign your return.
For 2018, you can't be using Turbotax Online. You can only prepare a 2018 return with the 2018 desktop software which you can purchase as a CD or download to install on a Mac or PC. When your return is ready to file and you print it, you will also print a cover page with instructions on where to mail the return and what to include.
