How to file with attached letter

Hello,

I am about to e-file (I am not late, living abroad) and want to attach an important message to the IRS regarding my return.

Do I e-file with Turbotax, and then send (via Post Office) my letter to the IRS with a copy of my return?

Or do I decline to e-file and choose to only "Print & mail" my return with my letter attached?

Thank you very much for your help.