Presumably, it would be treated the same as any other mail.

I receive perhaps one legitimate piece of mail per month in my mailbox at home, yet every time I open the mailbox, it is stuffed full of junk mail. I've asksd ny carrier to not place the junk mail in my box but she informed me that she has to. The senders are paying them to deliver it, so they do -- leaving me to have to constantly check the mailbox and throw it all away.