Have you hear of Brownells?

Brownell's is a reputable and well known firearms and gunsmith supply company. Guns, silencers, and machine gun parts are not illegal with the proper permits. Depending on the part(s), they are only sold to or through federally licensed dealers. Had you ordered a silencer they would require you to send them a copy of your federal permit and $200tax stamp.

I regularly get adds from them because I have ordered parts and equipment from them in the past. (not restricted items)

Maybe it didn't originate from Brownell's. I get emails like that from fake Amazon.

Rings a bell. Along with the usual junk mail ads for preppers/patriot supply companies and corporations pedaling the DOD and gun shops.

I bet it is fake a trick.