I dont mail anything anywhere, never have, never had a problem.
The brokerages give the IRS all the individual sales records, I dont see why we would need to send them as well, IRS already has it.
I make sure my gross proceeds match the 1099B to avoid any CP2000 notices and separate my summary lines into st covered, lt covered, st non covered, etc. so they land on the right page of the 8949
I summarize by ST Covered, LT Covered , ST Not-Covered , and LT Not-Covered if there are several. Then I refer to a .pdf attached (which is a copy of the broker sales pages). There is a special line in the drop-down box for attached pdfs that is specifically for the 8949. I have never sent a Form 8453 either.